To the north a narrow causeway called the Mill Dam (later Beacon Street) was built in 1814 to separate the Back Bay from the Charles. By the late 1800s, Bostonians had filled in the shallows to as far as the marshland known as the Fenway, and the original 783-acre peninsula had been expanded by about 450 acres. Thus the waters of Back Bay became the neighborhood of Back Bay.
Heavily influenced by the then-recent rebuilding of Paris according to the plans of Baron Georges-Eugène Haussmann, the Back Bay planners created thoroughfares that resemble Parisian boulevards. The thorough planning included service alleys behind the main streets to allow provisioning wagons to drive up to basement kitchens. (Now they're used for waste pickup and parking.)
Today the area retains its posh spirit, but mansions are no longer the main draw. Locals and tourists alike flock to the commercial streets of Boylston and Newbury to shop at boutiques, galleries, and the usual mall stores. Many of the bars and restaurants have patio seating and bay windows, making the area the perfect spot to see and be seen while indulging in ethnic delicacies or an invigorating coffee. The Boston Public Library, Symphony Hall, and numerous churches ensure that high culture is not lost amid the frenzy of consumerism.