The Grand Canal, crossed by three bridges (the Railway bridge, the Rialto and the Academy), together with the 45 "rii" (litlle canals) that flow into it, links all the sestieri (districts) of Venice to each other. The typical "rii" or "rieli" are mostly about 4 or 5 meters wide and can only be used by gondolas. The "rii" are nearly always flanked by narrow alleys called "calli".