A key is a tool for locking and opening a lock , e.g. B. a door lock or padlock . For this purpose, the key is usually inserted through the keyhole into the lock and this is opened by turning. Keys are used for burglary protection and access control .
Each key has a specific code. This lock coding or key coding describes the arrangement and combination of the holes or teeth (prongs) on the key bit. This means that the key can be assigned to one or more identical cylinders that correspond to this coding.
Historically, the most common key form is the tumble key . Its handle is known as a rhombus , mange , riding or reide . In earlier times this could be richly decorated. The part that grasps the locking device and ideally only fits a certain lock is called the beard . It is hard soldered to the stalk , cast or forged with it. The stalk can be solid (full spike) or hollow (hollow spike). In order to limit the depth of insertion of the key, a thickening is sometimes attached to the stalk (die, neck). All of this is intended to ensure that the corresponding lock can only be unlocked with this key or with an identical key. Because the task of a lock-key system is to protect a room, a vehicle or other objects from unauthorized entry, use or other access.
Keys were initially made of wood, later - as today almost exclusively - made of metal. They are usually connected to a key ring and several keys often form a key ring. Keys that are intended for use by several authorized persons are often kept in a key box.
History of lock and key
The historical origin of individual locking systems is described in the article lock (technology) . In the following section, however, the overall development is dealt with chronologically.
Prehistory and early history
From the late Bronze Age , for example, prehistoric soil finds of 30–50 cm long bronze keys in the form of sickle-shaped hooks were made in the pile dwellings in the Alpine region. They consist of two parts: the handle, which often has a ring closure, and the long, hook-shaped shaft, which is briefly bent inwards just before the end. The handle is sometimes twisted or decorated with plastic cross ribs. Elaborately worked keys also feature ducklings or stylized water birds. Often, however, the handles are missing entirely because they were made of organic material. Simple locks made of wood were operated with these Bronze Age keys: The bolt on the inside was pushed aside through a hole in the door.
In Egypt, locking techniques to be operated from the outside with the help of a push key were already known in the New Kingdom , which have also been documented several times in material and literary terms.
There are two different types of Greek keys: the temple key, the oldest type, which has been around since 1000 BC. Is in use and the laconic key, which has been in use since the 5th century BC. Is used.
The temple key is made of bronze , is about 40–50 cm long and was carried on the shoulder due to its size. In addition to inscriptions, it has also been preserved materially and was an attribute of priests and priestesses, for whom the temple keys represented a symbol of dignity and power. The handle of the temple key is worked and was mostly originally lined with wood or ivory . There are few surviving specimens of the Greek temple key, the associated wooden locks no longer exist, but could be reconstructed. With this lock, the key is inserted through a round, metal-framed keyhole and the bolt is pushed aside with a targeted push from the side. In order for the key to hit the attachment point better, the end was often turned wider. To close the lock again, the bolt was pushed back into place with a strap.
In the post-Homer period the key was perfected and the laconic key invented. The associated locks had a more sophisticated locking device and thus offered greater security. The laconic key was forged from iron. It has a straight shaft with a right-angled beard with three or four teeth. These lift corresponding locking blocks (βάλανοι / balanoi) in the wooden lock mechanism, hence the name Balanos lock . The end of the handle is often forged into a ring. On the associated lock, a wooden bolt was brought into the closed position from the outside by a strap and then artfully knotted. In order to be able to open the gate, the strap had to be untied so that the notched or bumped bolt could then be pushed back with the laconic key. At 10-14 cm, the laconic key is considerably shorter than the temple key. It is the model for Celtic and Roman keys.
In the Hallstatt period , the keys were made of wrought iron and served as grave goods. In their shape and size they were similar to the Bronze Age keys. They are quite long with 25–40 cm.
The keys of the Latène period are also made of wrought iron. The end of the handle is forged in a ring, and a die can also be found in isolated cases. The beard is shaped like a hook-shaped point and has three or more teeth. There are also T-shaped or anchor-shaped beards. At 6–30 cm, they are shorter than the keys from the Hallstatt period.
In addition to the division into Hallstatt and Latency keys, the Celtic keys are further divided according to appearance and function. Hook-shaped, S-shaped and laconic keys are considered to be simple key shapes. There are also keys to spring locks. This key-lock principle consists of the square spring pin or eyelet pin, which acts as a locking key, and the key with a frame-shaped forged beard. The locking key is inserted through a narrow slot. The springy wings of the lock are pressed together and snap together again after passing the opening. The locking key can then no longer be withdrawn, but can only be released by the frame-shaped key, the beard of which presses the springs back on.
The Sanzeno keys, named after the place where they were found, are also important. Due to their size (35–52 cm) and their characteristic beards, they occupy a special position among the Celtic keys. About 50 keys made of bronze or iron are known. The handle of the key is shaped differently, there is a kind of early die form, the beard has bizarre shapes. The Sanzeno keys are believed to be an early form of the lift and slide key. The key is inserted into the lock through an L-shaped keyhole. The tines grip from below into the wooden latch attached to the inside of the door, lift it up and push it to the side.
There are no known keys in the archaic era, but it is assumed that keys existed here too. Even with the Etruscans there are hardly any keys, these were only really known with the conquest by the Romans.
In the Roman Republic, the laconic key was used after the Greek model. This was used to lock house doors, for example. Chests were strapped and sealed. The seals were worn here on the middle finger of the left hand and called finger keys.
The Roman locking technology did not develop until the imperial era , i.e. around the turn of the century around the birth of Christ. The wooden bars were increasingly being replaced by metal structures. The so-called lift-slide keys after the opening movement can be recognized by the angled beard standing perpendicular to the handle. Countless specimens have been handed down as archaeological finds ( over 200 pieces were found in the Saalburg fort ). Their format and frequency suggest that not only doors but also storage units and boxes were locked in this way. The ridge of some small keys made it possible to carry them with you like a ring on your finger. Rotary keys, whose locks were technically more complex, were also used by the Romans. Larger keys were forged from iron, the smaller ones were cast from bronze, and those with bronze handles and wrought iron beards are also known. The keys were made in molds, the beard was given its shape by subsequent grinding or sawing. If the key was made of bronze and iron, the beard was cast using the lost wax technique. The Roman keys are between 2 and 25 cm long and have simple to very complex handles, for example in the shape of an animal. The beard has different numbers of teeth and can be broken.
Key from Israel
An important form of the key in Israel was the elbow key of the 2nd century BC. Chr. This is a kind of lift and slide key. The shaft is not straight but bent at a right angle and thus consists of an upper arm and a forearm. It has 5 teeth, is made of iron and, in the case of large keys, has a spherical handle made of wood. In the case of the associated lock, the bolt can no longer be moved after it has been closed, as it is held closed by a tumbler consisting of prongs that are pressed into holes in the bolt by one or more springs. The key is then inserted into the keyhole from the outside, the forearm grips the bolt, the beard lifts the tumbler and the bolt can be pulled out, using the entire key as a handle.
Anglo-Saxon keys (6th-11th centuries)
The Anglo-Saxon keys are mainly known as grave goods for the journey to the afterlife. However, there are only a few key findings and therefore little information. The keys are made of bronze, have an eyelet, a simple beard and were probably worn on a chain around the neck.
Viking key (8-11th centuries)
There are numerous finds of Viking keys. They are characterized by a simple openwork beard, a short shaft and a large, ornamental or animal-figured bow. Strongly stylized dragon patterns, braided patterns and anthropomorphic figures are also common. The Viking keys were made of bronze. They were not only objects of daily use, but also amulets and were worn on the body.
Early medieval and Carolingian keys
Very few keys have survived from the early Middle Ages , so knowledge about them is very sparse. They are made of bronze, are rather small at 6–13 cm and have a richly openwork bow. Lantern-shaped, decorative keys, which often represent a building or part of a building, are also rare. The beard is very simple and is often in the shape of a bird of prey head. It is a rotary wrench with ring and hallmark decoration.
Even Romanesque keys are very rare. Like the early medieval keys, they are made of bronze, are rather small (4–12 cm) and have a round bow. From the 12th century onwards, significantly larger wrought-iron keys with geometric shapes predominate. The strikingly long shaft tip protrudes far beyond the beard, making it easier to penetrate blocked keyholes. From the middle of the 12th century, the keys were up to 30 cm long, with cross-shaped patterns on the bow. The early Romanesque beards are small and simple and often grow large later. Sometimes they are broken up with geometric patterns. As in the rest of the Middle Ages, they are turning keys.
In the Gothic period , Gothic ornaments with arch, passport and leaf shapes became binding forms of the keys. The diamond shape of the bow, the ends of which are often enlarged, is characteristic. In addition, the keys often have knobs and, based on the window rosettes, rosettes. In the early Gothic period, the keys were made of bronze, 3–12 cm long and had a simple beard. In the high and late Gothic periods, the keys were made of wrought iron and were up to 50 cm long. The beard developed into a delicate, combed beard, which was often richly pierced with crosses and rectangles. In addition, in the Bamberg legal document of 1329, copying keys was made a criminal offense for the first time. The Regensburg guild regulations of 1393 also stipulated that the beards of the keys had to be adjusted so well that it was impossible to open the locks with a different key.
Renaissance key (15th - 16th century)
During the Renaissance , the emerging steel-cutting technique made it possible for the first time to sculpt figures from a forged piece of metal, which greatly expanded the possibilities of decoration. In general, the keys of the Renaissance are 4–30 cm long, are turning keys and have beards with fine incisions. In addition, the beards are star-shaped, cross-shaped or meandering. Different styles developed in the different regions of Europe. In Germany, Switzerland and Austria, keys with rolled ornamentation, which formed a handle made of double spirals, were typical. In Italy and France, on the other hand, the keys were decorated with grotesques , acanthus tendrils, chimeras , dolphins or mythical creatures of the sea. The key bow thus became an artful composition, the die was given the shape of an ancient capital . Particularly noteworthy are the Venetian keys. They have a round or oval bow, which is decorated with soldered ornaments in the shape of a rosette, which makes it resemble Gothic windows. The handle is provided with an eyelet or crown, the shaft is usually hollow. The beard is simple or has intricate, cross-shaped incisions.
Lantern handle key (16th - 18th century)
In the 16th century, the art of key and lock making reached its peak with the manufacture of lantern handle keys. The keys made in France in particular are real gems of blacksmithing. In order to be accepted into the guild as a master at that time, the journeyman had to produce a lock with a matching key as a masterpiece, which resulted in the production of true works of art. In addition, the keys created in this way are usually signed and dated. The key bow of the lantern handle key was stylized to a tower-like structure that looks like a lantern or a basket. This structure rests on a finely perforated rosette, which forms the center of the key. The outside is often decorated with masks or rings. The rosette rests on a richly openwork, square or rectangular base, which formed the die. This is followed by a short hollow shank with a fine combed beard, which can have up to 28 teeth. At the beginning of the manufacture of the lantern handle keys, the beard was flat, later it was hatchet-shaped. The fine elaboration was made possible by fine drilling and cutting technology, as well as steel turning work. Despite the delicacy of the keys, they were strong enough to set the lock mechanism in motion.
In the 17th century, heavy hand-forged iron chests finally appeared as safes for merchants, nobles and guilds for money, jewelry and valuable documents with the matching large-caliber keys. These chests often have a lock in the center of the lid. To open it, a complicated mechanism is set in motion by a simple twisting movement, which operates up to 25 latches. There was also a dummy keyhole at the front of the chest, while the real one is camouflaged in the chest lid. The keys that go with the chests are well-shaped with striking recesses on the beard, often in the shape of a cross or star.
In England in the 17th-18th Another new key type emerged in the 19th century. The newly emerged steel-cut technique made it possible to decorate in a previously unknown degree. Keys with heavily openwork, finely chased headballs and an exuberantly ornamented collar, shaft and beard could be made. This resulted in light but solid keys, for example for cupboards, chests of drawers, secretaries and jewelery boxes. The English keys were in great demand in England and on the continent, so they were exported in large quantities.
In the Rococo , the fashion of writing letters led to an impoverishment of the key. The keys were ousted by the manufacture of magnificent desks and secretaries with their rich decorations. Instead of ornate keys made of wrought iron, there are now mainly simple keys made of bronze. These are characterized primarily by their asymmetrical bow, which is decorated with tail patterns , foliage or C rocailles . The handles of the keys are simple in shape, the die is always spherical. The keys of the Rococo are turning keys 5–25 cm in length.
18. – 19. century
The 18th and 19th centuries were the last section of the hand-forged key. Due to the industrial revolution and the large number of new lock designs from America, which promised more security, only a few complex keys were made by hand. The guild trade was replaced by the manufactory in which the keys were mass-produced. In the second half of the 19th century, lock factories were also founded, in which the work process could be broken down into individual processes and machines could be used. Around 1870 there were numerous new lock factories, key foundries and suppliers. An important innovation was, for example, the malleable cast iron process in which the brittle cast iron was transformed into forged iron through long-term heat treatment (annealing for several days at 800–900 ° C). In addition, several keys could be cast and then processed at the same time. This process was much cheaper and replaced the hand-forged key.
There were many innovations, especially between 1770 and 1851, during which time around 70 models of various locks and keys were patented. One of the first patented locks was that of Robert Barron . The lock had two tumblers, i.e. moving parts in the lock housing, which release the bolt when the key is turned. Another pioneer was Jeremiah Chubb , who invented the multi-tumbler lock with six tumblers. With this lock there were already over 100,000 ways to push the tumblers aside. In addition, when a lock pick was used, a detector mechanism blocked the tumblers.
There was also a real competition between inventors and lock pickers. Who succeeded in cracking a lock that is considered safe under supervision expected high cash prices. Especially AC Hubbs 1851 caused a stir. He announced that he was able to open the Chubb lock, which was considered to be extremely safe and even known to the British government as not poop, within 30 minutes . He was able to prove this to a special committee: He opened the lock within 15 minutes and locked it again in another 7 minutes. He then tried his hand at the Brahman lock, which was considered unbreakable . He was given 30 days from the committee, of which he only needed 10 to unlock the lock. His method became known and published as Hobb's unlocking method . Many burglars saw this as valuable tips that they put into practice.
Of the numerous inventions made during this period, only Linus Yale's lock, which he invented in 1844, prevailed. Key and lock differed considerably from previous designs and were also suitable for industrial production. The Yale cylinder lock was initially hardly noticed at the Great Exhibition in London in 1851, only after the lock was improved by Yale's son Linus Yale Junior in 1864, the breakthrough came. With the Yale cylinder lock, the lock and bolt construction are separate. The key sets the cylinder in motion and this sets the bolt in motion, which means that the key can be kept very small and flat and there is a large number of possible locking variants. With older key-lock mechanisms, the bolt was always moved directly from the key.
In addition to precision mechanics, there is also microelectronics, which, for example, play an important role in the Kaba Nova key. This works through the interaction of mechanics and microelectronics. The microelectronics with stored access codes are housed in the Reide, and the contact field follows in the die, which establishes the connection to the electronics integrated in the door. The beard of the Kaba Nova also has a flat beard with extremely precise holes and millings. This results in over 25 trillion locking combinations.
Today's keys: special shapes and variants
With a master key several different locks can be unlocked. It is also referred to as a master key, central key or passepartout (from French passer , 'through' and partout 'everywhere'). The authorized user of a key has the power to use the key .
New building key
A new key is a tool that can be used to open doors without hardware or handles.
The picture opposite shows so-called bump keys. The profile notches are all uniformly on the deepest point. Most lock cylinders can be opened with such keys and a special striking technique. Locksmiths usually have such special keys in their tool kit.
There are tumbler and cylinder lock keys. Safe locks can sometimes only be unlocked by inserting two or more keys, each of which has a different person. This means that no user is alone when opening the door.
There are also dimple keys and reversible keys . Here, the side of the blank is drilled to different depths, the drilling pattern is identical on both sides - the key closes no matter how you insert it into the cylinder.
Special car keys
Car keys (ignition keys) often look similar to the serrated bit key and are usually symmetrical in shape. There are also special key forms, such as those from Ford . Renault keys have a small hole in the beard.
Berlin key / pass-through key
The Berlin key or pass-through key is a key with two beards. It is used to force house residents to lock again after entering or leaving the house. You first have to unlock it normally and then push the key through the keyhole. After you have locked it from the inside, you can remove the key again. The system was invented in 1912 by the Berlin key maker Johann Schweiger. The Berlin key was common in the first half of the 20th century, but is rarely used today.
In addition to mechanical keys, there are also magnetic card keys or electronic or electromagnetic systems, for example:
- with wireless transmitter (like the car key),
- with fingerprint recognition or
- with RFID technology. These are also known as transponders . These transponders are available as a card or key fob or integrated in a mechanical key, as is now common practice for car keys with an integrated immobilizer .
Video of a copying process
Keys from older locking systems, so-called bit keys, were always produced together with the lock. Duplicate keys can be created by filing a copy that is largely identical to a template. If the template is missing, e.g. B. because the key holder has not released it, it is possible to make the copy using an impression made of the original in soft clay, plasticine or plaster of paris. The copy is then filed and processed until the duplicate key fits comfortably into the impression. If there is no longer a key (or an imprint of the key) for a lock, making a key can be quite time-consuming, depending on how complicated the lock is.
Simple bit keys do not generally have to be a very precise fit, since in many older locks the beard determines whether it fits into the lock solely through its shape, the so-called curvature; however, the locking process works largely independently of the shape of the key. Keys with the curvatures common for simple room door locks are therefore available as finished spare parts.
Today, many simple keys that are used extensively on apartment doors or utility rooms can still be copied with a template that is clamped into a machine and scanned, the information being transferred to a tool that processes a blank . Service providers offer this work inexpensively and need a few minutes for it, provided that the appropriate blanks are in stock. The two pictures above show such machines.
More modern keys can no longer be copied in this way. For their production either no blanks are freely distributed or you need a code number or a numerical code that contains the information necessary to produce the duplicate key. A suitable milling machine is shown in the third picture above. Due to the formatting of the code, it can only be used in the applicable key system (type or manufacturer) and cannot be transferred to other systems or methods. The code can either be an identification number from a catalog kept secret by the manufacturer or it can relate directly to parameters of the key. In the case of keys that have certain electrical / conductive properties or that have magnets implemented, the codes indicate these properties. Without knowledge of the catalog or the meaning of the coded properties, it is very difficult, if not impossible, to generate a duplicate key even if you have a template. The advantage of this method is that duplicate keys must be ordered using modern means of communication and can be delivered by post.
Due to the large number of possible keys, modern key systems also offer the advantage that, by exchanging the lock cylinder, a single key or a subset of the circulating keys can become unusable, but the rest of the keys remain functional. The manufacturers offer various options here. Individual keys can also be created, whereby it is possible to specify which locks such a key may fit. One then speaks of a locking system . A security card is enclosed with this locking system, which can be used to produce duplicate keys or to order extensions to the locking system.
With these systems, the door can only be opened if two or more keys are used at the same time, in order to ensure that the door can only be opened by several key holders who are present. Either several locks are built into the door or a lock contains several lock cylinders. Combination solutions are then also possible, in which z. B. at least two of three keys are required to open. Due to the complex production of these locks, they are increasingly being replaced by electronic security units with access codes. For traditional reasons, however, they are still used in safes or in specially secured rooms. With newer designs, the keys no longer activate the actual mechanical locking process, but are only recognized and then set in motion built-in, electronically controlled automatisms, which simplifies the allocation of the keys and simplifies measures in the event of a key loss. Individual keys or their owners can be withdrawn from the group of authorized users without having to modify the locking system. It is also possible to determine for each key holder whether he or she is allowed to open the door alone or in company. In contrast to the access code, these systems offer greater protection against disclosure, in contrast to magnetic cards, they are more difficult to copy, cannot be accidentally deleted and mechanically less sensitive in daily use.
Symbolism and iconography
While in idioms and compound terms (such as key field , key qualification , key industry , key position , key stimulus , key novel ), the word key is often used in a figurative sense, mostly to characterize a target-oriented or understanding-building aid, the symbolic content is material or figurative (more symbolic ) Key was used and understood more as a legitimizing sign of the exercise of power.
Since the Greeks and Romans imagined the heaven and the underworld to be locked with gates, various gods also had keys, especially Janus (mythology) . The key as a sign of sovereign power in the sacred area has been encountered in the iconography on Greek grave reliefs since the classical period , where it can mainly be assigned to temple priests. Because of its size, the instrument was carried on the shoulder in the form of a rod bent twice at right angles ( laconic key ).
Christian symbolism and iconography
A passage from the Bible in the Old Testament ( Isaiah 21.22 EU ), where the keys of the house of David are placed on Eljakim 's shoulder, became a model for the meaningful and in its theological interpretations controversial scene in the New Testament ( Matthew 16.19 EU ), in which Jesus hands over the keys of the kingdom of heaven to the apostle Peter . Since the successors of Peter legitimized their power to bind and redeem, two keys appear in the papal coat of arms .
- Apostle Peter , on handing over the keys, see the previous section.
- Benno von Meißen (around 1010–1106), Bishop of Meißen. A legend tells that the church key, which he threw into the Elbe in order to prevent the emperor from accessing it, was swallowed by a fish and found in the fish belly after the bishop's return.
- Servatius of Tongeren , who is said to have received the keys of St. Peter through a miracle in Rome.
- Hubertus von Lüttich , patron saint of locksmiths, see also Hubertuskey .
- Some other venerated figures are depicted with a non-compulsory key attribute, such as Genoveva of Paris (in her legend she opens the city gates to free prisoners) and Blessed Gamelbert (with the keys of his investiture ).
- The key rings of St. Notburga von Rattenberg , St. Petronilla and the biblical Martha mark their housewife role.
Emblematic in Renaissance and Baroque
In the emblematic of the 16. – 17. In the 20th century, the key can have the following meaning, in addition to the papal meaning: the power of prayer, redemption through Christ, the virtues of the housewife and secrecy. In Cupid's hand it is accompanied by the lines: " ... only one who suits me finds the innermost part of my heart ... ". The key federation stands for the diversity of talents.
The handover of the keys as an act of surrender or homage
The ceremonial handing over of the keys of conquered cities and fortresses to the victor probably only became common in the Middle Ages. We see one of the oldest representations of this process on the Bayeux Tapestry (after 1066), the most famous example in art history in the Handover of Breda (1625) by Diego Velázquez, and in the modern era, finally, an extremely unceremonious version, turned from the ritual to the existential in the form of the bronze group "The Citizens of Calais" by Auguste Rodin (1895).
The city keys handed over after conquests often remained in the possession of the victor, while in homage that did not constitute an immediate act of surrender, the keys were then tacitly returned to their previous use. In other cases, magnificent specimens were made especially for such ceremonies, as, for example, Jérôme Bonaparte decreed in 1808.
This ritual was resumed during the "transfer of power" from town halls to fools during the carnival days, which is often carried out in today's custom with symbolic keys . Furthermore, the handing over of key fakes, which have also been enlarged in a media-effective manner, is a common action at building openings and inaugurations.
Countless people and corporations have kept one or more keys in coats of arms or logos, some of them up to the present day . In the vast majority of cases, the motif is derived from the attribute of St. Peter , who refers to the patron saint of the coat of arms leader or the patronage of the local church.
Marital power of keys
The key has been a symbol of the wife's power of disposal (power of keys ) over matters relating to her own household since ancient times. " Taking a woman's key" ( claves uxori adimere ) was synonymous with divorce. Medieval and early modern depictions often show wives with a bunch of keys on their belts.
As a sign of their dignity, chamberlains wore a key to the princely private chambers visible on their official costume. In the 18th century the chamberlain key was transformed into a symbolic showpiece made of gilded bronze.
Key in popular belief
In popular belief, the key is used as a carrier of magical powers in a wide variety of applications. It supposedly heals illnesses and injuries, protects against dangers and serves as an instrument when questioning the future. The obvious symbolism of key / phallus and lock / vagina is related to "superstitious" behavior patterns that were used during pregnancy and childbirth. The keys that have been inherited over several generations have been given particular power. In amulet form were saints attributes (of Peter, Ulrichs-, Hubertus key ) spread in Styria of Reiner grace key . The so-called Frais key , worn on a chain around the neck, should protect against cramps.
Whistle concert on keys
Until the first half of the 20th century, hollow keys were widespread, in which the hollow stalk (the tube) met a pin (thorn) in the lock for better guidance when closing. You can whistle on this tube of the hollow key. If a theater or music premiere led to a theater scandal, the audience could spontaneously pick up the house key and express their displeasure by whistling. "A whistle rings out of a key" is how Paul Gurk describes such a protest in his 1934 novel Berlin . Today the possibility of whistling about keys has been forgotten due to the lack of a cavity in modern keys. This is why historical statements about intended interference with house keys may no longer be understood, as in 1913: The summer of the century by Florian Illies , who cited the public's protest against Arnold Schönberg's modern music with house keys as an alleged "rattle" and rattle (" there is hissing, laughter, keys clattering ") misinterpreted.
Literature (on history and symbolism)
- Hermann Diels : Ancient technology . 6 lectures. Teubner, Leipzig / Berlin 1914. Chapter L: Antique doors and locks, pp. 34–49.
- Adalbert Erler: Key (as a symbol). In: Concise dictionary of legal history. Volume 4, Berlin 1990, p. 1443.
- Heinrich Pankofer: key and lock. Munich 1973.
- Jean-Josef Brunner: The key through the ages. Bern / Stuttgart 1988.
- Martin Müller: Keys and Locks in Roman Everyday Life - Selected Finds from Colonia Ulpia Traiana. In: Dangerous Plaster: Crime in the Roman Empire. Exhibition of the Xanten Archaeological Park. von Zabern, Mainz 2011, pp. 19–40.
- Hans Bächtold-Stäubli: Concise dictionary of German superstition . Volume 7, Berlin / Leipzig 1936, column 1221.
- Sigrid Canz: Key and lock as carriers of meaning. In: Schlosserkunst. Photo guide of the Bavarian National Museum in Munich. 1976.
- Lock, key. In: The New Pauly. Volume 11, Stuttgart 2001, Col. 186-189 (Keys in antiquity)
- Manfred Welker: Historical keys and locks in the Germanic National Museum in Nuremberg. Inventory catalog. Nuremberg 2014.
- Jean-Josef Brunner: The key through the ages. Paul Haupt Publishing House, Bern / Stuttgart, 1988.
- Key in tenancy law. Website of the Berliner MieterGemeinschaft e. V., accessed on July 9, 2010.
- Michael Keuter, Alexander C. Blankenstein: Keys / Locking System (WEG) / 1 key coding. Retrieved February 24, 2020 .
- Brunner, pp. 30-48.
- Benjamin Hinson: The Egyptian Item. In: Journal for Egyptian Language. Volume 140, Issue 2, 2013, pp. 129-131.
- Brunner, p. 9; Otto Königsberger: The construction of the Egyptian door , 1936, pp. 61, 63.
- Homer: Iliad. 12,455 f .; Odyssey , 21,241.
- Brunner, pp. 27-29. The New Pauli. Sp. 187.
- Brunner, pp. 27-29. The New Pauli. Sp. 187.
- Brunner, pp. 50-67.
- The subject - ARTE carom ( memento from June 15, 2009 in the Internet Archive ), accessed on July 9, 2010
- The New Pauly. Volume 11, p. 188.
- Brunner: Key. Fig.p. 8 and 11.
- Hiltgart L. Keller: Reclam's Lexicon of Saints and Biblical Figures . Stuttgart 1968, p. 215.
- Lexicon of Christian Iconography. Volume 6: Iconography of the Saints. Freiburg 1974, column 348.
- Arthur Henkel, Albrecht Schöne: Emblemata. Stuttgart 1967, Sp. 1819, 1335-1339, 1750.
- Contrary information in the symbol literature is consistently unproven.
- Rodin: The Citizens of Calais (detail)
- 1367, Cardinal Albornoz presented the Pope with a large number of keys from conquered cities after the reconquest of the Papal States (Erler, hand dictionary, Sp. 1444). In 1815, Tsar Alexander I had 93 keys from 25 conquered cities hung as trophies in the Kazan Cathedral (W. Bruce Lincoln: Sunlight at Midnight. St. Petersburg and the rise of modern Russia. New York 2002, p. 110; Alfred Löhr: The Bremen Keys in St. Petersburg. In: Bremisches Jahrbuch. 95, 2016, pp. 11-18).
- Rolf-Dietrich Müller: Two "golden" keys. A gift from the city of Paderborn to the King of Westphalia. Only digital. Retrieved May 10, 2016.
- Examples: Bremen coat of arms , flag and coat of arms of the canton and the city of Geneva .
- Daniel Jütte: The State Gate. Thresholds and Power in Western History. 2015, p. 105.
- Cicero, Phil. 2,69.
- W. Brauneder: Key power, marriage law. In: Concise dictionary of legal history. Volume 4, Berlin 1990, Sp. 1446-1450.
- To the whole section: Canz, pp. 37–43.
- Florian Illies: 1913: The summer of the century. 4th edition. S. Fischer, Frankfurt am Main, 2016, pp. 53, 54 and 96.