In the last years of the 18th century, when space in the city became scarce, a series of major changes began to transform the urban landscape. In that period of expansion, the architect Charles Bulfinch, who for more than a quarter of a century was also the head of the town government, skillfully transformed an 18th-century English town into a 19th-century American city. Bulfinch designed the central portion of the present State House (1795–98), above Boston Common on Beacon Hill. The construction of the State House on that site led to the conversion of the upland pastures of Beacon Hill into a handsome residential district that has survived with relatively little change. Between the State House and Charles Street are several streets, including famous Louisburg Square, filled with many houses by Bulfinch and other leading 19th-century architects. The area is protected by historic district legislation and has been designated as the Beacon Hill Historic District.

As pressures of population in the 19th century caused a growing demand for land, hills were leveled to fill in the coves. So much new land was created that the former peninsula became an indistinguishable part of the mainland. Fill on both sides of the narrow neck that connected the peninsula with the mainland created a new South End. The waterfront was greatly extended, and the Back Bay was dammed (1818–21) to create tidal power for new mill sites. A causeway along the dam extended west from Boston Common to Sewall’s Point, the present Kenmore Square, thus furnishing more-direct communication with the mainland. The filling of the Back Bay flats just west of the common created land that in the 1830s was laid out as the Public Garden. That became a splendidly planted area with an artificial pond that is still traversed by swan-shaped excursion boats in the summer.

The Back Bay mill basins never developed as their promoters had envisioned, partly because the construction of railway lines through them in the 1830s hindered the flow of water. The basins became a foul-smelling nuisance, and the Massachusetts legislature in 1857 authorized the filling of that extensive area. The adopted plan provided for four new streets parallel to the Mill Dam (Beacon Street), to be intersected by cross streets. Commonwealth Avenue, running west from the Public Garden and 200 feet (60 metres) wide with a park between its roadways, created the atmosphere of a Parisian boulevard. Since there were no hills left to cut down, gravel had to be brought in by train from pits some distance away in Needham. By the end of the 19th century the Back Bay was completely filled and built up with houses that were subject to uniform height limits and setbacks. The region today presents a picture of American architecture that is as consistent for the second half of that century as Beacon Hill is for the first. Although many Back Bay houses have been converted to apartments, offices, schools, or other uses, the region has retained a good deal of its original character, and further changes are subject to architectural control.

The Emerald Necklace

When the Back Bay was nearing completion during the 1880s, the American landscape architect Frederick Law Olmsted developed an imaginative large-scale design for the city’s parks. It linked the common, the Public Garden, and Commonwealth Avenue with Franklin Park south of Roxbury by way of a string of parks—including the Back Bay Fens—that combined water, woods, and meadows along an open park known as the Fenway, which followed the Muddy River between central Boston and Jamaica Plain. Included in that park system, known as the Emerald Necklace, was the Arnold Arboretum, a botanical outpost of Harvard University in Jamaica Plain. About the turn of the 20th century, institutions such as the Boston Symphony Orchestra, the New England Conservatory of Music, the Museum of Fine Arts, and the Harvard Medical School and hospitals moved west to locations near the Back Bay Fens. The completion in 1910 of a dam that kept the harbour tides out of the Charles River converted the remaining unfilled portion of the Back Bay into a body of fresh water. The Charles River basin—surrounded by parkland and patterned on the Alster River basin in Hamburg, Germany—remains one of the most handsome, distinctive, and popular features of Boston.

Annexations

With the end of the American Civil War in 1865, large numbers of Boston residents, many of them Irish immigrants, abandoned the congested waterfront districts and moved into the nearby suburbs. Soon many of those new districts sought to annex themselves to the city of Boston in order to obtain such services as water, sewers, schools, hospitals, police security, and fire protection. In 1868 Roxbury became a part of Boston; Dorchester followed two years later; and in 1873 Charlestown, Brighton, and West Roxbury were also annexed. The city’s population jumped from 140,000 in 1865 to 341,000 in a decade—an increase of more than 200,000 people. Once a small community of some 1.2 square miles (3.2 square km) of land, Boston is now nearly 40 times its original size. The new communities, known as neighbourhoods, became parts of the city’s ward system and were populated at first by groups of Irish Americans. Gradually, however, as new ethnic groups moved into Boston after the turn of the 20th century, they usually moved into one neighbourhood or another, making it distinctly their own. In that manner, South Boston and Charlestown were soon identified as distinctly Irish, the North End and East Boston as Italian, the Mattapan district as Jewish, and the Roxbury area as African American. Central Boston continued to be regarded as traditionally Anglo-Saxon Yankee.