Here there is a very important group of monuments: the "rectangular"
temple and the "round"
one. The ancient sources, above all Orazio and Varrone,
permit their identification.
In fact, the authors remember two temples corresponding to these for the position: the rectangular temple of the mythical founder of the city, Tiburnus, or for others of Albunea, the Sibilla Tiburtina near the falls of the Aniene, in the sacred forest; and the round one commonly said of Vesta.
In the temple of the Sibilla there were preserved
the statue of cult, miraculously appeared from the water of
the river, and the book of the prophecies. Both the buildings
were turned into churches in the Middle Ages.The first one
became the church of S.Giorgio (since the year 978 it has
been mentioned in documents), the second one became the church
of S.Maria Rotonda.
This use made possible that the two temples were not completely despoiled of their marbles and stones as it happened to some other monuments that almost until the end of the past century were sacked of their materials in order to be re-used in the construction of new buildings.
Once, in fact, the old Roman buildings were pits from which columns, marbles, bricks came for being later used in several ways in the new houses under construction. Just have a walk through the Medieval and historical part of the city, and you'll see them! Nowadays, the two temples, the rectangular and the round, are on the terrace of the restaurant "Sibilla", and they are open to tourists. However, it's above all from the Gregorian Villa that you can appreciate the spectacular location of the two temples. In fact, they are nearly on the edge of the ravines created by the falls of the river Aniene: a challenge of the man's abilities to build up in places where nature puts limits. For this reason, when the two temples were built, it was necessary to create an artificial platform on which raising them; near the cavern of Albunea (of which Orazio says) and the sacred forest of the founder of the ancient Tibur: Tiburno.