Combined Locks is part of the Rideau Canal, a chain of rivers, lakes, and waterway structures built under the direction of the British military between 1826 and 1832 to serve as a supply route and recognized as an outstanding example of 19th century construction and engineering ingenuity. Many original canal structures still survive. At Combined Locks, the original flight of three locks was completed in 1831, then replaced in 1974 by a single automated lock when a fixed bridge was built over the canal to handle increasing automobile traffic, while the old locks were preserved for viewing. A defensible lockmaster's house built in 1841 also survives at the lockstation. At Smiths Falls, the Rideau River descends almost 11 metres in less than 1/2 kilometre, so canal engineers created an upper detached lock connected to a long basin and three lower locks emptying into the next reach, with a waste weir and a 7-metre-high stone arch dam on the north side of the basin to control water level.