an atrium (or several). In later Roman history the atrium was sometimes also replaced by a peristyle, and rain-gathering with piped water from an aqueduct. The urban houses of poorer Romans might lack atriums entirely; but from (mainly Pompeiian) survey data, atriums, peristyles, or both are found in almost all Roman homes over 350 square meters in size, most over 170 square meters, and some over 50 square meters. Etymology The etymology of "cavaedium", "cavum aedium", and "atrium" is debated. These terms are thought by many to be synonymous; others have argued that one term includes the impluvium and the other does not, but are not agreed upon which. Varro gives classical etymologies: "The hollow of the house (cavum ædium) is a covered place within the walls, left open to the common use of all. It is called Tuscan, from the Tuscans, after the Romans began to imitate their cavædium. The word atrium is derived from the Atriates, a people of Tuscany, from whom the pattern of it was taken." For more modern etymologies, see :Wiktionary:atrium. Uses Light, water, air and cooling Roman townhouses rarely had windows, as they often had very little exterior wall. Where present, windows were placed above eye-level, and they were small and contained clathri, window lattices. The compluvium provided most or all of the light to the atrium, its alae, and the adjacent cubiculums. The doorways of the cubiclums were usually arranged to maximize the light, and when present, the alae were often needed to let light into the rooms flanking the tablinum. Traditionally, the atrium collected rainwater. Most atria had compluvium roofs, which sloped inwards towards the hole in the center of the roof; these shed rain water into the impluvium (pool) underneath (the impluvium was usually the same size and shape as the compluvium hole). The water in the impluvium then slowly seeped through the porous bottom of the impluvium into a water storage cistern below. Water for household use could be drawn up in buckets via the puteal (a lidded cylinder set over a hole in the top of the cistern as a wellhead). In dry weather, water drawn from the cistern could be thrown into the impluvium to evaporatively cool the cistern and the house, and drive a draft. In wet weather, impluvium overflow would generally run out the front door into the street, which was much lower than the interior