Like the monumental Propylaea, the Erechtheum had to overcome irregularities of terrain, and its south and east walls stand some 9 feet above its north and west walls. Although the Porch of the Caryatids is the more famous, the North Porch, with its elegant carved architectural ornament, is perhaps the more deserving of praise. Within the temple was both an ancient wooden idol (a "xoanon") and an olive wood statue of Athena Polias (Athena of the City). Like the great statue of Athena in the Parthenon, this statue also received a new robe in the Panathenaic festival. The Erechtheum was also where every year, four girls (from wealthy families) spent several months within the house of the Arrephoroi, in service to Athena.