A four-poster bed is a bed with four vertical columns, one in each corner, that support a tester, or upper (usually rectangular) panel. This tester or panel will often have rails to allow curtains to be pulled around the bed. There are a number of antique four-poster beds extant dating to the 16th century and earlier; many of these early beds are highly ornate and are made from oak.
Four-poster beds were developed for several practical reasons. Bedrooms often had drafts and could be cold at night: the curtains could be closed to help keep the occupant of the bed warm. The curtains also helped to give privacy to the sleepers, since servants and bodyguards often slept in the same room, especially in the case of royalty, served by a special group of servants of the bedchamber (usually noble courtiers), lords and ladies of the bedchamber, esquires of the body, etc. In the mediaeval era and up to the 18th century beds were items of furniture on which great personages and royalty made public appearances and held court, thus they were designed to impress. A four poster bed with backboard and tester allowed extra space from which to display and hang expensive fabrics and heraldic decoration.
A four-poster bed is referenced in the Mishnah, which was redacted in the 3rd century CE.
Four-poster beds are mentioned in numerous Irish sagas and were recorded in early Irish manuscripts. In the 12th century tale of Acallam na Senóradh, in the wooing of Credhe, Cael ua Nemhnainn cites in a poem "Four posts round every bed there are, of gold and silver laid together cunningly; in each post's head a crystal gem: they make heads not unpleasant [to behold]", when speaking of a fairy-mansion on the Paps of Anu, in Co. Kerry.
An example of 16th-century four-poster resides in Crathes Castle, which was made for the original castle owners in the Burnett of Leys family.
Four poster beds are different from other types of beds because they have vertical columns in each of the four corners of the bed, supported by an upper panel. Traditionally, curtains were drawn around the bed to keep the occupants warm at night, in those days before central heating was the norm.
...If one spread a sheet as a canopy over the frame of a four-post [kinof] bed...