A VISION FOR A BRIDGE: Plans for a crossing between the city of Brooklyn and lower Manhattan dated back to the early 1800's. When the East River crossing was planned, Brooklyn, with about 400,000 residents, was still more rural than urban. The city of New York - which at the time consisted only of Manhattan - had twice as many residents, and the bridge was seen as a solution to overcrowding in Manhattan while spurring development in Brooklyn. The bridge would enable people and goods to cross the East River quickly, regardless of weather conditions.
From The Great Bridge by David McCullough: A bridge over the East River, joining the cities of New York and Brooklyn, had been talked about for nearly as long as anyone can remember… But nothing was done. The chief problem was always the East River, which is no river at all technically speaking, but a tidal strait and one of the most turbulent and in that day, especially, one of the busiest stretches of navigable salt water anywhere on earth. "If there is to be a bridge," wrote one man, "it must take one grand flying leap from shore to shore over the masts of the ships. There can be no piers or drawbridge. There must be only one great arch all the way across. Surely this must be a wonderful bridge."