In the 12th century, the Libero Comune di Verona (the Free Municipality of Verona) decided to build some fortifications to defend part of the south west of the province; this had become necessary since the natural defences provided by the Mincio river, by the morainic heights and the marshland of the Tione were no longer sufficient to repel incursions from Brescia and Mantua. And so the castles of Ponti sul Mincio, Monzambano, Valeggio, Villafranca, Custosa and Sona were constructed, and the fabbrica del Serraglio was created, within the already existing municipality. This gigantic work consisted of a long curtain wall interspersed with 150 (or perhaps 200) towers which linked together the Borghetto as well as the four castles of Valeggio, Gherla, Villafranca and Nogarole, and which was sixteen kilometres in length. The Serraglio continued to carry out its role to the end of the 15th century. Today, the Serraglio no longer exists; the ditches have been filled in and are now cultivated, while the walls are in a ruinous state or were destroyed. Testimony to the ancient work of fortification remains only the ruins of the Gheria and the foundations of the walls which are uncovered every time excavations run close to their original alignments.