Security, and keeping possessions under lock and key, goes back thousands of years. A lock found in ancient ruins near Nineveh, is thought to be 4,000 years old. The Romans kept valuables in chests locked by a key worn as a ring. And about 500 years after the Roman empire collapsed, locksmiths in England were making all-metal lock and key systems. Double-acting pin tumbler locks used today, were patented in 1848, so have been used commonly since, for over 160 years.