than a quarter of a mile posed an obstacle to navigation at Smiths Falls. A natural depression to the south of the river was used to create a flight of three locks, known as Combined Lockstation today. The natural course of the river was dammed to create a basin upstream of the locks. At the upper end of the basin a fourth (detached) lock was constructed. A mile below the Combined Lockstation is a flight of two locks called the Old Slys Lockstation. This station is named for the original settler at this location, William Sly. A dam and waste weir control water levels upstream of the locks. Defensible lockmasters' houses were built at all three stations in Smiths Falls. The house at Old Slys was built in 1838 and the houses at Combined and Detached around 1842. Only the house at Combined has a second storey, which was added late in the 19th century. The defensible lockmaster's house at Detached Lockstation was torn down in 1894. Entry of the railways In the 1850s the major railway companies were looking to build main trunk lines linking Toronto, Kingston and Montreal. The two major companies at the time, the Canadian Pacific Railway and the Grand Trunk Railway, were competing for the easiest routes to lay track. At one point a fledgling third national railway, the Canadian Northern Railway (CNoR), was also trying to squeeze itself into the busy Montréal-Ottawa-Toronto corridor. For a number of geographical reasons, and also due to the proximity of the Rideau Canal, the town of Smiths Falls became a major focal point for both the CPR and the CNoR. Each used a mix of existing regional rail lines and new construction to build their networks. CP purchased the 1859-era Brockville and Ottawa Railway, a line from Brockville-Smiths Falls-Sand Point/Arnprior with a branch Smiths Falls-Perth (the latter joining CP's Ontario and Quebec Railway line to Toronto). CNoR built a 1914-era main line from Ottawa-Smiths Falls-Sydenham (to join an existing Bay of Quinte Railway line extending westward via Napanee-Deseronto). By 1887, the CPR had extended its Toronto-Smiths Falls mainline to reach Montréal; in 1924, 1600 CPR workers were employed in Smiths Falls. This gave the town direct rail lines in half a dozen directions (towards Toronto, Ottawa, Montréal, Brockville, Napanee and Arnprior) on two different rail companies. During World War II, Axis prisoners of war (POWs) were transported to