Canals were once the autostradas of medieval Milan, transporting timber, marble, salt, oil and wine into town. The largest of them, the Navigli Grande, grew from an irrigation ditch to one of the city's busiest thoroughfares by the 13th century. Five cruises run from April to September; the most popular, the Conche Trail, loops round the Naviglio Grande and Naviglio Pavese back through the dock.