The temple of the Sybil, rectangular, dating from the II century B.C., is in ionic style. It consists of a travertine base witch supports the lateral walls with semicolumns. This temple was probably the one dedicated to the Sybil; the adjacent circular temple was dedicated to Vesta, or else to Hercules Saxanus, who was particularly venerated in Tivoli.
In the Middle ages this temple was transformed into the church of St. George, no longer visible today. From the area of the temples( the ancient roman acropolis) one can enjoy a beautiful view of Villa Gregoriana and of the Cascades located just underneath Ponte Gregoriano.