Arrived in Rome in 1660, when Pietro da Cortona, Borromini and Bernini were at work in this city, he was at first Bernini's pupil and collaborator in the enlargement of Palazzo Chigi-Odescalchi (iter 7) . In 1683 he constructed S. Marcello al Corso's façade , in 1702 the arcade overlooking the church of S. Maria in Trastevere and the fountain in front of it (iter 5); the Cybo Chapel in S. Maria del Popolo, Ginetti Chapel in S. Andrea della Valle and the completion of the baptismal fountain chapel in S. Peter are good examples of his composition composure. He completed Palazzo di Montecitorio (iter 7), begun by Bernini, for which he had conceived a grandiose project that afterwards remained undone; he proposed to raise a church inside of the Coliseum and to re-arrange the Borghi and the access to Piazza S. Pietro, but none of these projects were carried out. As much as Bernini and Borromini influenced him, he interpreted the baroque's dynamism in a more peaceful way, thus becoming the starting point for Rome's eighteenth century's architecture. In a numerous series of essays and writings, besides of illustrating architecture a hydraulics technical topics, he gave news on works performed by him and on those he had projected. He had two sons:

Baldassare (Chiasso 1658 – Bruna, Moravia, 1729), sculptor, stucco-decorator and architect, at work in Moravia and Poland;

Francesco (Rome 1668 - Castel Gandolfo 1708), architect, author of the reconstruction of the interior of the Basilica dei SS. Apostoli in Rome . Francesco's son, Mauro, (1701-1769), projected in Rome the church and the convent of the Ursulines and the Chapel to beato Sauli in the church of S. Carlo ai Catinari.

One of Carlo's brothers, by the name of Giovan Battista , had two sons which were also architects: Girolamo (active between 1690 and 1714), author of the façade of Frascati's Dome; Carlo Stefano Fontana (active around 1700), that built S. Clemente's façade and convent (1711) in Rome (iter 4) .