1564, in order to replace those from the 12th-14th centuries, as part of his policy of making Grosseto a stronghold to protect his southern border. The design was by Baldassarre Lanci, and construction began in 1565. Until 1757 the exterior was surrounded by a ditch with an earthen moat. There were two main gates: Porta Nuova on the north and Porta Reale (now Porta Vecchia) on the south. The walls are now used as a public park and walking area. Religious architecture Cathedral The Romanesque cathedral, the main monument of the city, is named for its patron St. Lawrence, and was begun at the end of the 13th century, by architect Sozzo Rustichini of Siena. Erected over the earlier church of Santa Maria Assunta, it was only finished in the 15th century (mainly due to the continuing struggles against Siena). The façade of alternate layers of white and black marble is Romanesque in style, but is almost entirely the result of 16th century and 1816–1855 restorations: it retains decorative parts of the originary buildings, including Evangelists' symbols. The layout consists of a Latin cross, with transept and apse. The interior has a nave with two aisles, separated by cruciform pilasters. The main artworks are a wondrously carved baptismal font from 1470–1474 and the Madonna delle Grazie by Matteo di Giovanni (1470). The campanile (bell tower) was finished in 1402, and restored in 1911. Churches in the city centre Church of San Francesco. Situated in its homonymous square, it was built in the 13th century, initially an important Benedictine, later Franciscan convent. The complex underwent several restorations and reconstructions: the bell was rebuilt in the first half of the 20th century. Very characteristic is the wooden tabernacle that stands on the front and inside there are works of art from various historical periods. At the center of the cloister stands the characteristic Pozzo della Bufala (Well of the Buffalo) in travertine; another well is located in the square outside the church. Convent of Clarisse. Located on strada Vinzaglio, the convent is annexed to the Church of Bigi. The convent of Clarisse and the church of Bigi are now deconsecrated. The entire complex is characterized by the probable medieval origins, which was followed by a series of restorations in Baroque style in the 17th century. Today the convent hosts the Museolab Città di Grosseto and the university. Church of San Pietro. The