Cathedral and Museo Diocesano are The five-domed cathedral of San Pietro was built in the 15th and 16th centuries on the site of an earlier Romanesque church. Below it is the crypt of the original church, dating from the 11th and 12th centuries; the porch was added in 1836. City Walls and Gates The well-preserved 15th-century walls that surround Treviso are not the first; Treviso was a Roman city and the Romans fortified it from the earliest days. The River Sile flows alongside the walls, and together with the River Cagnan, it was used to further protect Treviso from attack. The waters were diverted into canals that encircled the city and were designed so they could also be used to flood the surrounding lowlands, making a siege difficult. The present walls, strengthened by earthworks, were built by the Venetians, as you can guess from the winged lions on the imposing gates. Treviso was Venice's major stronghold protecting it from invasions from the north. Museo Civico di Santa Caterina. The status - and location - of Treviso's municipal museum has been the subject of some confusion for almost a decade, as its original building on Borgo Cavour has been undergoing a long (and some say endless) restoration.. The artistic highlights of the Museo Civico are the frescoes by Tommaso da Modena and Girolamo da Treviso, and paintings by Bellini, Titian, Lotto, Pisanello, and many other artists. At the southwest corner of the old town, the Dominican church of San Nicolò is a spacious Gothic church built in brick during the 13th and 14th centuries. It has round piers and an unusual vaulted timber roof, which has been restored. On the high altar is Madonna Enthroned by Fra Marco Pensaben and Savoldo from 1521, and the tomb of Senator Agostino Oningo is by master sculptors Pietro and Tullio Lombardi dating from 1490. What makes them so outstanding, even in this city where there are so many examples of his work, is their personality, even humor. Canals and Water Mills; Two rivers encircle Treviso, and in addition to their confluence here, their waters have been contained into a series of canals and tiny waterways that wander picturesquely through the city. Houses rise directly from their water and it flows under the arched foundations of others. Every bridge reveals another vignette of balconies above the water. Adding to all this is an occasional waterwheel, remnant of those that once drove mills throughout the city. You'll see them as you walk around Treviso, but there is one quite near the Pescheria, the fish market.Visit Pescheria (Fish Market),One of the oldest and least changed quarters in Treviso includes the colonnaded buildings of the Buranelli and the convent of the Camaldolese nuns. Piazza dei Signori stands In the center of Treviso is the picturesque Piazza dei Signori with the Palazzo dei Trecento, built in the late 1100s and once the seat of Treviso's government, and the 15th-century Palazzo del Podestà with the tall Torre del Comune. The Palazzo Pretorio, a Renaissance palace, now houses the town council. Between Piazza dei Signori and Piazza del Duomo runs Via Calmaggiore, Treviso's main street, lined by fine 15th- and 16th-century houses. Although only three blocks long, it has a number of buildings with decorated facades and lunettes above their arched doorways.