Points of Interest > Don Blockhouse

In response to growing fears by York residents about the likelihood of an invasion by the Mississaugas, displaced from their lands and enraged by the recent murder of Mississauga Chief Wabukanine by a solider in the Queen’s Rangers, Peter Russell (then Administrator of Upper Canada) ordered the construction of a blockhouse near the Parliament Buildings in 1799.

Sir Edmund Wyly Grier (1862-1957), An East End View of York (Toronto) Upper Canada in 1810 (looking west from Don Blockhouse east of foot of Berkeley Street), 1812, Toronto Public Library, TRL, Historical Picture Collection, Acc. JRR 545.

The blockhouse was typical for the period: a two storey log structure roughly 100 feet square, with the upper storey offset as seen in the picture. A signal light on the roof guided ships to York's harbour.

The area around the blockhouse was considered in its time to be particularly susceptible to “miasmas”—disease-producing vapours caused by decomposing organic matter. Until the germ theory of disease gained credibility in the late nineteenth and early twentieth centuries, low, wet places such as marshes, where decomposition processes were especially evident, were blamed for a host of ailments including the “ague” or lake fever. Characterized by alternating symptoms of severe fever and shaking chills, the ague was an almost inevitable, if rarely fatal, aspect of life in Upper Canada in the late eighteenth and early nineteenth centuries. Now understood as a strain of malaria, a disease spread by the bite of the Anopheles mosquito, at the time the ague was thought to result from inhaling ‘bad air’ (hence mal/aria).

With its position overlooking the massive reaches of Ashbridge’s Bay marsh, the Don blockhouse gained a reputation as a particularly “miasmatic” or unhealthy location. In 1803, for example, Sir Isaac Brock reported in a letter to military secretary James Green that the soldiers quartered in the Don blockhouse “are falling ill of the Ague and Fever in great numbers” while the garrison at the west end of town “continues in perfect health.” Ironically, despite mistaken theories about the origin of disease, fears of miasma were not entirely misplaced. The slow-moving waters of the Don marshes would have provided an excellent breeding ground for mosquitoes, and efforts made to avoid these “unhealthy places” and to shut out the dangerous “night air” often had the effect of shutting out mosquitoes as well.

The Don blockhouse was destroyed during the American invasion of York in 1813.

Text: Jennifer Bonnell and Lost Rivers


Toronto Historical Association. A Glimpse of Toronto's history: Opportunities for the Commemoration of Lost Historic Sites (Toronto: Toronto Historical Association and the Maps Project, City of Toronto Urban Development Services, 2002), MPLS #051.

Sir Isaac Brock to James Green, 29 July 1803, in Edith G. Firth, The Town of York, 1793-1815: A Collection of Documents of Early Toronto (Toronto: Champlain Society, 1962), 72.

Valencius, Conevery Bolton.  The Health of the Country: How American Settlers Understood Themselves and Their Land (New York: Basic Books, 2002). (on miasmas)

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