In 1814, the Boston and Roxbury Mill Corporation built the Boston & Roxbury Mill Dam across the back bay. The dam was intended to harness the power of the tides to create energy for potential mills. Developers also built a toll road on top of the dam. This road bypassed the narrow land bridge, called Boston Neck, that was Boston’s only connection to the mainland at the time.
However, the contractors didn't consider the environment impact of the dam, and the bay soon became dirty and stagnant. The project was also a financial disaster due to greatly underestimated construction costs. Developers originally predicted the project would only cost $250,000 but it ended up costing $700,000. To further compound the problem, only three mills were ever built near the damn, which brought in only $6,000 in annual revenue.
Realizing that the state of the bay was a considerable problem, the city began filling in the 700 acres of the bay in 1857. For fifty years, day and night, trains brought gravel from Needham. When the Great Fire of 1872 destroyed much of the city, rubble from the fire was used for fill. The project finally reached completion in 1882. This new land nearly doubled the size of Boston peninsula.