The living quarters of a castle with a bergfried are separate, often in a lower tower called a palas. (An English-style keep combines both functions of habitation and defence.) Consequently, a bergfried could be built as a tall slender tower with little internal room or vaults and few if any windows. The bergfried served as a watchtower and as a refuge during sieges (at least if the siege was relatively brief). The distinction between a bergfried and a keep is not always clear-cut, as there were thousands of such towers built with many variations. There are some French keeps with only austere living quarters, while some late bergfrieds in Germany were intended to be habitable (Piper 1900).