He participated in Bernini's Funereal Monument for Pope Alexander VII Chigi, found in St. Peter's Basilica. He also was responsible for the Angel with the scourge, based on a sketch by Bernini; this is one of the angels on the Ponte Sant'Angelo in Rome. He is said to have sculpted the horse and the lion for Bernini's Fountain of the Four Rivers in Piazza Navona. Lazzaro also sculpted the statue of Benignity for the tomb monument of Clement X in St. Peter's. The tomb was designed by Mattia de' Rossi (1684) and the other sculptors who worked on this project were Ercole Ferrata (who sculpted the pope) and Giuseppe Mazzuoli (who sculpted the statue of Clemency). He also completed some of the saints in the roof-line of the external colonnades of Piazza San Pietro. He also participated in the decoration of the church of San Pietro Martire in Ascoli Piceno. Morelli also designed the aedicule (an outdoor shrine) outside the church of San Francesco in Piazza del Popolo of Ascoli Piceno. Set against an external wall, it was an altar that could be used by the condemned as they were led to execution.