It is believed that the concept of bunk beds began in Europe between 1400-1500. Wealthy lords traveled across country largely via carts, which were designed for sleeping. The cart/bed was formally named the “truckle bed” which is also known as the trundle bed. It refers to any bed that can be stored underneath another bed.
During Elizabethan times, servants often traveled with their masters and they slept on the lower bed, which is the origin of the expression to “truckle under,” which implies a lower social status. This was later changed to “knuckle under” as one had to get down on one’s knees in order to “knuckle under.” That expression later came to mean obeisance to one’s master.
It is not known exactly how the bunk bed got its name, but it may have its roots in the military, as these beds were often used in places with limited floor space, such as ships and army garrisons. They are also commonly found in dormitories, summer camp cabins, hostels, children’s rooms, prison cells and university residence halls.