Largest reconstructed 18th-century French fortification in North America, located on Cape Breton Island, Nova Scotia. The fortress contains original stone drain systems, a countermine tunnel built through marshy ground, and the burial chapel of the duc d'Anville, a member of the Rochefoucauld family with ties to the Knights Templar.
About This Site
The Fortress of Louisbourg is the largest reconstructed 18th-century French fortification in North America, situated on Cape Breton Island approximately 300 miles northeast of Oak Island. Originally constructed beginning in 1713 following the Treaty of Utrecht, the fortress served as the capital of the French colony of Ile Royale and as the primary military and commercial hub for French interests in the North Atlantic. At its peak it was one of the most heavily fortified positions in the New World, defending lucrative fishing grounds and the approaches to the St. Lawrence River.
The fortress fell to British forces during the first siege in 1745, was returned to France under the Treaty of Aix-la-Chapelle in 1748, and was captured again and systematically demolished by the British in 1760. Today it is operated by Parks Canada as a National Historic Site, with extensive reconstructions of the original French buildings, fortifications, and underground structures including casemates and a cross-shaped countermine tunnel built through marshy ground in its original 18th-century condition.
Connection to Oak Island
In Season 7, Rick Lagina and historian Doug Crowell traveled 300 miles northeast to Louisbourg after dendrochronology results dated a red spruce timber from the bump-out structure at Smith's Cove to 1741, more than two decades earlier than the slipway and U-shaped structure. The date aligned with the first siege of Fortress Louisbourg in 1745 and supported naval historian Chipp Reid's theory that the French may have moved a vast fortune from the fortress to Oak Island in the early 1740s as the military situation deteriorated.
Parks Canada historian Sarah MacInnes guided Rick and Doug through the original 18th-century French structures. In the chapel, they visited the burial site of Jean-Baptiste de La Rochefoucauld, the duc d'Anville, a French naval commander and member of a noble family with documented ties to the Knights Templar. The duc d'Anville led a massive 1746 expedition to recapture Louisbourg from the British, but the fleet was devastated by storms and disease before reaching its objective, and the duc himself died and was buried under the altar of the fortress chapel. The Rochefoucauld family name also appears on a mysterious 14th-century map connected to Oak Island.
In the casemates, Rick and Doug discovered an original stone drain system strikingly similar to the box drain structures found at Smith's Cove. MacInnes then showed them the countermine tunnel, a 180-foot cross-shaped passage built through marshy ground and still in its original 18th-century condition. The tunnel demonstrated that the French possessed the engineering capability to construct underground passages in wet environments like those theorized on Oak Island, and that the drainage infrastructure at Smith's Cove was consistent with French military engineering practices of the period.
Fieldwork Notes
Visited during Season 7 by Rick Lagina and Doug Crowell. Parks Canada historian Sarah MacInnes guided the team through the original French structures. Key observations included the duc d'Anville burial chapel, original stone drain systems in the casemates resembling Smith's Cove box drains, and the 180-foot countermine tunnel built through marshy ground demonstrating French engineering capability in wet conditions. The visit established direct parallels between French military construction at Louisbourg and underground structures found on Oak Island.
