England's longest man-made waterway, the Grand Union Canal runs 137 miles from London to Birmingham, with 158 locks and three tunnels. Formed from independent canals joined in 1929, its main line opened in 1796 during "canal mania", funded by the wealth of the Empire and the slave trade. Canals beat the poor roads of their day, but separate ownership and mismatched sizes hampered trade, and railways, industrial decline and motorways ended commercial traffic by the 1960s. Enthusiasts led by the Inland Waterways Association saved the network, and today it is a tourist attraction, a living museum and a haven for nature and the arts.