in spring 1368 visconti allied with cansignorio della scala of verona, and attacked mantua, still ruled by ugolino gonzaga. the situation was settled later in the year through an agreement between him and emperor. two years later he besieged reggio, which he managed to acquire from gonzaga in 1371. the following war against the este of modena and ferrara raised again papal enmity against the milanese, now on the part of gregory xi. in 1370, he ordered the construction of the trezzo bridge, then the largest single-arch bridge in the world.