§196. The Atrium.--The _ātrium_ (§188) was the kernel of the Roman house, and to it was given the appropriate name _cavum aedium_. It is possible that this later name belonged strictly to the unroofed portion only, but the two words came to be used indiscriminately. The old view that the _cavum aedium_ was a middle court between the _ātrium_ and the _peristylium_ is still held by a few scholars, but is not supported by the monumental evidence (§187). The most conspicuous features of the _ātrium_ were the _impluvium_ and the _compluvium_ (§188). The water collected in the latter was carried into cisterns; over the former a curtain could be drawn when the light was too intense, as over a photographer's skylight nowadays. We find that the two words were carelessly used for each other by Roman writers. So important was the _impluvium_ to the _ātrium_, that the latter was named from the manner in which the former was constructed. Vitruvius tells us that there were four styles. The first was called the _ātrium Tūscanicum_. In this the roof was formed by two pairs of beams crossing each other at right angles, the inclosed space being left uncovered and thus forming the _impluvium_ (Figs. 42, 43). The name (§188) as well as the simple construction shows that this was the earliest form of the _ātrium_, and it is evident that it could not be used for rooms of very large dimensions. The second was called the _ātrium tetrastylon_. The beams were supported at their intersections by pillars or columns. The third, _ātrium Corinthium_, differed from the second only in having more than four supporting pillars. It is probable that these two similar styles came in with the widening of the _ātrium_ (§191). The fourth was called the _ātrium displuviātum_. In this the roof sloped toward the outer walls, as shown in the cinerary urn mentioned in §189, and the water was carried off by gutters on the outside, the _compluvium_ collecting only so much as actually fell into it from the heavens. We are told that there was another style of _ātrium_, the _testūdinātum_, which was covered all over and had neither _impluvium_ nor _compluvium_. We do not know how this was lighted; perhaps by windows in the ālae. [Illustration: FIGURE 44. SMALL HOUSE AT POMPEII]