The Pietrasanta Duomo, or the St. Martin's Collegiate Church, dating back to 1223. The exterior is covered with white marble of the area, with a sloping front profile. In the right transept opens a door topped by a sculpted lunette depicting St. John the Baptist, fourteenth-century by Bonuccio Pardini. The coats of arms on the facade are reminiscents of the Genoa and Florence domination, as well as a large coat of arms of Leo X. The rose marble is attributed to Riccomanno Riccomanni (XIV century). The plant is a classic Latin cross with three naves with a transept. The works preserved date back to different eras, but the period that has most influenced the present appearance is that of the Grand Duchess Christina of Lorraine, who in 1627 commissioned Florentine artists the renovation of the Church (with works by Matteo Rosselli, Francesco Curradi, Jacopo Vignali Pietro Dandini, Sebastian Bitozzi, Jacopo Chiavistelli and Alessandro Cominotti), while the apparatuses sculptural were treated by Giovan Battista Stagi, Stagio Stagi and Ferdinando Tacca. It goes back to the previous century marble pulpit, a valuable work by Donato Benti and Lorenzo Stagi (1508). The walls and ceilings were painted with various subjects in color or chiaroscuro by the Milanese painter Luigi Ademollo between 1823 and 1825. The octagonal dome was originally (1453) but was rebuilt in 1820. In a chapel to the right major, it is the venerated relic of Our Lady of the Sun, a painting on wood with a Madonna and Child with Saints (1424). The Baptistery, located to the right of the Cathedral, dating from the seventeenth century. Contains two baptismal fonts, works by Bonuccio Pradini, Donato Benti and Niccolò Civitali. The vault and the walls are scenes from the life of Christ and the Virgin, works by Pietro Cavatorta.