CAVAEDIUM  , in

architecture, the Latin name for the central hall or court within a Roman house, of which five species are described by Vitruvius . (I) The Tuscanicum responds to the greater number apparently of those at Pompeii, in which the timbers of the roof are framed together, so as to leave an open space in the centre, known as the compluvium; it was through this opening that all the light was received, not only in the hall itself, but in the rooms round . The rain from the roof was collected in gutters round the compluvium, and discharged from thence into a tank or open basin in the floor called the impluvium . (2) In the tetrastylon additional support was required in consequence of the dimensions of the hall; this was given by columns placed at the four angles of the impluvium . (3) Corinthian is the term given to the species where additional columns were required . (4) In the displuviatum the roofs, instead of sloping down towards the compluvium, sloped outwards, the gutters being on the outer walls; there was still an opening in the roof, and an impluvium to catch the rain falling through . This species of roof, Vitruvius states, is constantly in want of repair, as the water does not easilyrun away, owing. to the stoppage in the rain-water pipes . (3) The testudinatum was employed when the hall was small and another floor was built over it; no example of this type has been found at Pompeii, and only one of the cavaedium displuviatum .