I always wondered why the steep stairs on these old homes in NYC. Well now I know. I thought they were perhaps afraid of flooding but..
While the high entrance looks like flood defense, NYC brownstone stoops (from the Dutch stoep) were actually built to escape 19th-century street filth. With thousands of horses lining the roads, street-level mud, manure, and dust were constant hazards. Raising the main entrance kept the elegant parlor floor clean, dry, and smelling fresh.
The high stoop also established a clever social and structural layout. It allowed servants and delivery workers to use a discreet street-level door tucked under the stairs to access the kitchen, while formal guests climbed the grand steps above. Plus, raising the main floor created space for basement windows, letting natural light and fresh air reach the lower levels.