Legend has it that on the night of the Nativity, the emperor Augustus consulted the Tiburtine Sibyl and asked her if any greater ruler existed, or would ever exist. He was shown a vision of the Virgin suckling the Christ Child, and heard a voice proclaim 'Ecce ara coeli' ('This is the altar of Heaven'). The church of Sta. Maria in Aracoeli was later built on the spot where the vision occurred.