The Church of the Most Holy Annunciation in Zagarolo was commissioned by Pompeo Colonna and his wife Orinzia and the cornerstone laid on 18th October 1580 by Pompeo's brother, Cardinal Marcantonio Colonna. The building project, entrusted to the Barnabite Father Gian Lorenzo Binago, included a convent for his congregation, adjacent to the church. The first Mass was celebrated on 25th March 1599 by Father Binago.
Work on the church commissioned by Marzio Colonna included the fine plasterwork by Andrea Carene and Ottavio Grisolati (17th century).
The church was built on a sandstone rise with a Latin Cross floor plan, circular cupola and octagonal bell tower. The portal is flanked by granite columns with capitals that may be relics from an Imperial Roman building.
The cross vaulted aisle holds communicating side chapels which open onto the nave. The most important paintings include: The Birth of Mary and the ovals of the Evangelists by Pietro da Cortona and The Annunciation, Flagellazione and Resurrection by Marcantonio dal Forno. The 9th century Roman-Byzantine fresco is also noteworthy, as is the Madonna of Divine Providence by Scipione Pulzone da Gaeta and 17th century wooden choirstalls.