For many centuries, and perhaps back to Homer, Western society slept in two shifts. People went to sleep, got up in the middle of the night for an hour or so, and then went to sleep again. Thus night — divided into a “first sleep” and “second sleep” — also included a curious intermission. “There was an extraordinary level of activity,” Ekirch told me. People got up and tended to their animals or did housekeeping. Others had sex or just lay in bed thinking, smoking a pipe, or gossiping with bedfellows. Benjamin Franklin took “cold-air baths,” reading naked in a chair.
Via Improbable Research.
According to Wikipedia, this phenomenon is called segmented sleep:
Segmented sleep, divided sleep, bimodal sleep pattern and interrupted sleep are modern Western terms for a polyphasic sleep pattern found in medieval and early modern Europe and many non-industrialised societies today, where the night's sleep is divided by one or more periods of wakefulness. This is particularly common in the winter.