The "auditorium" (literally "place for hearing" in Latin) was the area in which people gathered, and was sometimes constructed on a small hill or slope in which stacked seating could be easily made in the tradition of the Greek Theatres. The central part of the auditorium was hollowed out of a hill or slope, while the outer radian seats required structural support and solid retaining walls. This was of course not always the case as Romans tended to build their theatres regardless of the availability of hillsides. All theatres built within the city of Rome were completely man-made without the use of earthworks. The auditorium was not roofed; rather, awnings ("vela") could be pulled overhead to provide shelter from rain or sunlight.