By 1500, all of Italy was busy reorganizing its defensive walls to cope with the power that had arisen from the new tools of offense: cannons. In these years the situation in Cagliari also had to be decisively revised; the medieval towers had lost most of their function, having wall thicknesses now incapable of supporting the weight of enemy broadsides. The pressing Turkish insidiousness from the sea had to be met with more adequate structures. The Spanish rulers thus decided to employ renowned architects to carry out surveys and study the reinforcement of the fortifications. The Swiss engineer Jacopo Palearo known as “Fratino,” a well-known designer of many European fortified squares, entered the scene in Cagliari at the behest of Philip II of Spain. In addition to plans involving the Bastoni extensions he designed the Plazuela burrow in order to achieve faster transit of the guns and artillerymen to the bulwark to the east. Sixty-eight meters long in the main arm, it was dug into the rock starting from the site now referred to as Piazza Carlo Alberto as a service tunnel, running underground on a route that heads eastward for about 24 meters passing under the flight of stairs leading to Piazza Palazzo, intercepting a conduit 55 meters long and parallel to Via Martini, and then dividing into two arms, one of which is directed toward the eastern walls. In later centuries the tunnel was used in various ways and, in the Savoy era when the court of Carignano moved to Cagliari in the sovereign’s retinue, it probably served to provide security for the king’s residence. Currently the branches of the route are barred and to the north the route is interrupted due to modern masonry. The burrow intersects three times with pre-existing cisterns, two of which predate the period of its implementation.
