At least six keys were recovered at Masada from levels the excavators apparently associated with the occupation of the Sicarii. Would a small group of people living close together and uniquely bound by a common cause feel the need for security from each other—even as they defended themselves on an isolated mesa in the middle of the desert? What do these keys tell us about the people who used them on Masada, and what significance do they hold for the modern observer? This chapter explores the types and functions of typical locking devices in the ancient Mediterranean world from 2000 B.C. down to Byzantine times and sets the cultural backdrop for their use at Masada.