real breakthrough as a composer came with his first collection of 12 concerti for one, two, and four violins with strings, L'estro armonico (Opus 3), which was published in Amsterdam in 1711 by Estienne Roger, dedicated to Grand Prince Ferdinand of Tuscany. The prince sponsored many musicians including Alessandro Scarlatti and George Frideric Handel. He was a musician himself, and Vivaldi probably met him in Venice. L'estro armonico was a resounding success all over Europe. It was followed in 1714 by La stravaganza (Opus 4), a collection of concerti for solo violin and strings, dedicated to an old violin student of Vivaldi's, the Venetian noble Vettor Dolfin. In February 1711, Vivaldi and his father traveled to Brescia, where his setting of the Stabat Mater (RV 621) was played as part of a religious festival. The work seems to have been written in haste: the string parts are simple, the music of the first three movements is repeated in the next three, and not all the text is set. Nevertheless, perhaps in part because of the forced essentiality of the music, the work is considered to be one of his early masterpieces. Despite his frequent travels from 1718, the Ospedale paid him 2 sequins to write two concerti a month for the orchestra and to rehearse with them at least five times when in Venice. The orphanage's records show that he was paid for 140 concerti between 1723 and 1733. Opera impresario In early 18th-century Venice, opera was the most popular musical entertainment. It proved most profitable for Vivaldi. There were several theaters competing for the public's attention. Vivaldi started his career as an opera composer as a sideline: his first opera, Ottone in villa (RV 729) was performed not in Venice, but at the Garzerie Theater in Vicenza in 1713. The following year, Vivaldi became the impresario of the Teatro San Angelo in Venice, where his opera Orlando finto pazzo (RV 727) was performed. The work was not to the public's taste, and it closed after a couple of weeks, being replaced with a repeat of a different work already given the previous year. In 1715, he presented Nerone fatto Cesare (RV 724, now lost), with music by seven different composers, of which he was the leader. The opera contained eleven arias and was a success. In the late season, Vivaldi planned to put on an opera entirely of his