During its construction in 1832, Merrickville was an established village that authorities thought may be at risk for invasion. To avoid such a scenario, Colonel John By decided to have a blockhouse built as a masonry and timber defensive structure for the lock station.

This blockhouse was, and still is, the largest on the Rideau Canal and the second largest in all of Canada. Today it exists as a museum.

Photo: Doktor Ellis, CC-BY-SA-3.0