Francesco Borromini (Bissone Lugano 1599-Rome, Italy, 1667) was a Baroque architect, and rival of Gian Lorenzo Bernini.

Son of stone mason Giovanni Domenico Castelli, Borromini began his career as a stone mason himself, and soon moved to Milan to study and practice this activity. When in Rome (1619) he changed his name (from Castelli to Borromini) and started working for Carlo Maderno, his distant relative, at St. Peter's. When Maderno died, he joined the group of Gian Lorenzo Bernini, with whom he completed Maderno's Palazzo Barberini [1].

In 1634 he had his first personal work, the reconstruction of the church of San Carlo Borromeo (some authors say it is here that he changed his name).

Borromini's works include:

San Carlo alle quattro fontane [1]
Sant' Agnese in Agone
Sant' Ivo della Sapienza [1]
San Giovanni in Laterano
Chiesa Nuova
Cappella Spada [1]
Sant'Andrea delle Fratte
San Giovanni in Laterano, basilica (nave)
Oratorio de' Filippini
Collegio de Propaganda Fide [1]
Santa Maria dei Sette Dolori
San Giovanni in Oleo (restoration)
Palazzo Giustiniani (with Carlo Fontana)

For Sant'Agnese in Agone, he reverted the original plan of Girolamo Rainaldi (and his son Carlo), which previously had main entrance on via dell'Anima. Façade was expanded to include parts of the bordering Pamphilii palace, gaining space for the two bell towers (each of which has a clock, as in St. Peter's, one for Roman time, the other for tempo ultramontano, european time).

Borromini lost this work before this was ended due to the death of the Pope Innocent X. The new Pope and Prince Camillo Pamphili called back Rainaldi, but this one didn't change very much and the church is mainly considered a notable expression of Borromini's concepts. These concepts have also being considered as a solution for Bernini's vain search in St.Peter's façade.

He was also called "Bissone", by the place in which he was born.

In the summer of 1667, Borromini, suffering from nervous disorders and depression), committed suicide after the completion of the Falconieri chapel (the main chapel) in S. Giovanni dei Fiorentini, where he was buried.

Karl Baedeker's 1883 Guide of Central Italy reports: Maderno with Borromini and Carlo Fontana were the leaders of that band of Artists who conspired to rob architecture of its fitting repose and (...) substituted a turbulent unrest

Francesco Borromini was featured on the 100 Swiss Franc banknote current in the 1980s.