The lock originated in the Near East, with the oldest known example discovered in the ruins of Khorsabad's palace near Nineveh known today as Iraq [3]. It is of the type known as a pin tumbler or, because to its widespread use in Egypt, an Egyptian lock, and is possibly 4,000 years old [3]. It is made up of a huge wooden bolt that secures the door and is perforated by a slot with multiple holes in its upper surface (figure 5) [4]. A door assembly has multiple wooden pins that are positioned to drop into these holes and grasp the bolt [3]. The key is a large wooden bar in the style of a toothbrush, but instead of bristles, it contains upright pegs that match the holes and pins [5]. Inserted into the huge keyhole beneath the vertical pins, it is easily lifted, allowing the pins to clear and the bolt with the key to be moved back [5].
Figure 6: Different Roman Keys and Locks
The next step in the development of keys occurred in Ancient Rome, where engineers and innovators considerably improved on the designs of Egyptian wooden locks [3]. The Romans were able to develop much stronger and smaller locks, with keys that were light enough to be carried on person, by employing iron and bronze (figure 6) [3]. In terms of the shape of the keys, one significant invention transformed their appearance forever [4]. This design was used for 17 centuries following the fall of the Roman Empire, with only slight changes in appearance. Skeleton keys can still be located in homes built before the 1940s [4].
Figure 7: Modern Day Lock and Key
Linus Yale made a significant contribution in 1848 when he invented a pin tumbler lock based on an adaption of the ancient Egyptian principle [5]. In the 1860s, his son Linus Yale, Jr. invented the Yale cylinder lock, with its compact, flat key with a serrated edge, which is currently the most well-known lock and key in the world (figure 7) [5]. The serrations lift the pins in the cylinder to the right heights, allowing the cylinder to be turned [5]. The amount of pin height combinations (typically five), along with the warding effect of the crooked key and keyhole, provide an almost infinite number of variations [5].