The construction of the first city walls must have taken place after 1179, the year in which Frederick I issued a decree allowing Drudo, the Bishop of Feltre, to strengthen the defences of the town. The position of the medieval walls, with irregularly spaced towers, is preserved in some places, and is indicated by the layout of later buildings. The war between Sigismund of Austria and the Venetian Republic in 1487 led to a modernising of the defences in line with the new techniques of siege warfare, and was undertaken (though never completed) by the engineer Dionsio da Viterbo. In 1489, under the governorship of Girolamo Cappello, the section between the Imperial Gate and a medieval tower further to the east was completed.
In 1493, under the rule of Domenico Contarini, the semicircular tower between the Imperial Gate and the Pusterla Gate was added. Under Francesco Marcello, in 1494, the Pusterla Gate and the tower immediately to the east were finished. Both towers were demolished between the end of the 18th century and the early 19th century. In 1496, the walls were extended as far as the Oria Gate to the east. Finally, in 1502, under Francesco Bollani, the construction of the walls to the south and the restoration of the Oria Gate were completed. After the destruction of 1509 – 1510 the walls were hurriedly repaired but were only used for customs purposes.