During the war, British officers constantly worried that the Americans would block the St. Lawrence River, which forms part of the Canada–US border. If that had occurred, there would have been no British supply route for Upper Canada, where most of the land battles took place, and British forces would likely have had to withdraw or to surrender all of the western British territory within a few months. British officers' dispatches after the war exhibited astonishment that the Americans never took such a simple step, but the British were not willing to count on their enemy repeating the mistake and so they commissioned the Rideau Canal, an expensive project that connects Kingston, on Lake Ontario, to the Ottawa River, to provide an alternative supply route to bypass the part of the St. Lawrence River along the border. The settlement at the northeastern end of the canal, where it joins the Ottawa River, later became the city of Ottawa, Canada's fourth-largest city and its capital, which was placed inland to protect it from an American invasion and was then known as the "defensible back-country." Because the population far from the St. Lawrence shores was negligible, the British, in the years following the war, took great lengths to ensure that back-country settlement was increased. They settled soldiers, initiated assisted-immigration schemes, and offered free land to farmers, mostly tenants of estates in the south of Ireland. The canal project was not completed until 1832 and was never used for its intended purpose.