Between 1840 and 1930, the Square Mile was in its golden age. It was a time of great prosperity for the Anglophone bourgeoisie, who had left the overpopulated and noisy fortified old city for the fresh air higher up around Mount Royal. This commercial aristocracy controlled the country’s destiny and two-thirds of its wealth. The Anglophone upper society residents of this quadrilateral of approximately one square mile engaged in fox hunting, and dined on gourmet meals in villas inspired by Florence and the Scottish Highlands. But the serenity of the area was disrupted by the construction of Windsor Station and the department stores along Sainte-Catherine Street. Starting in 1900, the future downtown Montreal was gradually taking shape. With the 1929 crash, ostentatious tastes were on the wane and it became a challenge to pay for the staff needed to maintain the mansions. The Golden Square Mile princes migrated westward, toward Town of Mount Royal and Westmount. In their wake, streets were laid and apartments and office buildings erected in the neighbourhood, opening the door to real estate speculation.
In a mere 50 years, the Square Mile transitioned from its golden age to urban decay. The wave of industrialization at the turn of the 20th century led to the transformation of bourgeois homes. With little regard for the urban environment, the ‘50s and ‘60s saw the destruction of architectural heritage and shaped a different urban space. Dozens of mansions disappeared, replaced by housing units, rooming houses and apartment buildings of varying degrees of attractiveness. Only about 30% of the bourgeois homes survived, north of Sherbrooke Street.