Fresh from its victory against the British in the War of 1812, the United States was eager to secure its northern border. Lake Champlain had been the entry point for several British invasions, so it was the logical place to build a fort. In 1818 the work was commenced on the massive structure. The design called for it to have 125 cannons within its 30-foot-tall walls. There was only one problem with it: the fort was on the Canadian side of the border.
The location was due to a surveying error, placing the fort three-fourths of a mile to the north of the 45th parallel — the USA/Canada border, as defined by the Treaty of Paris. This accidental invasion of Canada, unlike the accidental invasions of Liechtenstein, cost the invading country more than red faces. The error was not discovered until two years into construction and only after $275,000 had been spent on the project.
Left with no other option, the workers abandoned the partially-completed fortress. For the next twenty years, the abandoned site became a prime source for free building materials for area residents. This continued until 1842 when the property officially became US territory under the provisions of the Webster-Ashburton Treaty. By this point, however, it made more sense to build a new fort, rather than try to make something out of the abandoned structure. The result was a new Fort Montgomery, while the abandoned site received the unofficial name Fort Blunder.
Fort Blunder remained the property of the United States until the 1920’s, when it was sold at public auction. The property passed from owner to owner. In 1999, the current owners, the Victor Podd family, tried to sell the property on eBay. They received a bid for $5 million, but the deal fell through without a sale. It is still available for sale today, if you are interested in owning your own partially-completed fort.