[1] The original church was built in the 5th century, on the ruins of the Pretorium which tradition holds was the prison that held the martyred Sant'Alessandro.

[3] Its construction for the Barnabite order began in 1601 to a design by Lorenzo Binago.

The first church of Sant Alessandro was demolished, along with the nearby San Pancrazio.

The first stone of the church was laid on 30 March 1602 by Cardinal Federico Borromeo.

By early 1627, the center dome had developed deep cracks and was demolished.