Boston's grandest residential district was, until the 1850s, an actual back bay — a stinking, mud-bottomed tidal estuary west of the Common. The city spent forty years filling it in with gravel hauled from Needham by train, then laid out the grid of Commonwealth Avenue, Marlborough, Beacon, Boylston, and Newbury streets and sold off the lots. The result is the largest and best-preserved Victorian neighbourhood in North America.
Commonwealth Avenue, a 220-foot-wide boulevard with a tree-lined central mall, is the spine of it — modeled directly on the boulevards of Haussmann's Paris, with elaborate brownstone facades by every fashionable architect of the day. The mall makes a fine half-mile walk from the Public Garden to Kenmore Square.
The big civic set-pieces of Back Bay are Copley Square (Trinity Church, Boston Public Library, John Hancock Tower), the Christian Science Plaza (the Mother Church and the Mapparium), and the Prudential complex. Newbury Street is the shopping street; Boylston has the marathon finish line; Beacon Street has, in season, magnificent magnolias.