One of Rome's most elegant water features is located in the center of this Piazza Mattei, the Fontana delle Tartarughe, also known as the Tortoise Fountain. The fountain itself was designed by Giocomo della Porta at the end of the 16th century, but it was Bernini who added the tortoises in 1658.

Designed by Giacomo della Porta with bronze figures by Taddeo Landini this fountain has a great appeal: the four youths are not angels: real life comes out of their lithe bodies, while the tortoises (added in 1658, most likely by Bernini for Pope Alexander VII) hint of some mysterious ceremony.

The Matteis controlled the Isola Tiberina, the island in the Tiber River, and so had hegemony over the entire left bank. This family used the site and the material of the Theater of Balbus to construct the first of a series of buildings, known in the mid 16th century as the Isola Mattei.

Buildings such as these indicated great economic power deriving from trade and commerce. The family used the experience and ability of the Jews to construct these buildings and, in return, offered them whatever protection they needed.