The history of locks and keys goes back several thousand years to Ancient Egypt. These early locks and keys originally used wood and other easily accessible, natural materials, so they offered very little protection against intrusion. Because these locks were not very reliable, they were used more as an indicator of tampering.
The next evolution of keys came from Ancient Rome. The Roman age improved the original Egyptian designs by using precious metals such as iron, bronze, silver, and gold. By using metals, Romans were able to create stronger, yet smaller locks and keys. Although an improvement from the wooden locks, these expensive locks still provided little protection against intrusion. They were instead used as a symbol of wealth, influence, and nobility.
Today, a majority of locks use flat keys. Developed in the 1800s, these flat keys are easy to manufacture, and easy to replicate in large numbers. Throughout its evolution, the new designs of locks today provide the strongest protection by using lever and pin tumbler locks.