It’s been estimated that in the 12th and 13th centuries as many as 100 stone towers rose above the rooftops of Bologna, reaching heights of 100m (330 ft.). They were probably built as places of refuge and for offensive purposes, and they implied no small amount of wealth, since it took as long as 10 years and enormous expense to put the successively thinner layers of stone and masonry in place. Some 20 towers remain, and the most famous are these two slender medieval skyscrapers that lean tipsily but poetically just east of Piazza Maggiore. The Garisenda rises 49m (162 ft.) and leans about 3m (11 ft.) from perpendicular; the Asinelli stands 102m (334 ft.) tall and inclines almost 2.5m (7 1/2 ft.). Garisenda is off limits, but a climb up Asinelli’s 500 steps reveals Bologna’s finest aerial panorama, a sea of red-tile roofs and the green hills beyond.