Before the Brooklyn Bridge was built, people could only cross the East River from Manhattan to Brooklyn and back by boat.
Before the Brooklyn Bridge and the subway system were invented (in that order), the only way to cross the East River was by boat.
Before the Brooklyn Bridge was built, there was no way to cross the East River from Brooklyn to Manhattan, or Manhattan to Brooklyn, except by boat. Traveling between them was extremely inconvenient. The Brooklyn Bridge changed all that. It made commuting much easier; it was now possible for people to live in Brooklyn, but work in Manhattan. It is not a coincidence that the five boroughs -- which at the time were separate cities -- incorporated into one city in 1898, only 5 years after the bridge opened. The Brooklyn Bridge helped bind the boroughs together into one city.
No, it doesn't. The Brooklyn Bridge crosses the East River and connects the borough of Brooklyn to the borough of Manhattan. Note that the East River is not a true river, but a tidal strait. It connects to the ocean on both sides. It flows south from the bay known as the Long Island Sound, down the east side of Manhattan and the west side of Queens and Brooklyn, and into the Atlantic Ocean at New York Harbor.
a bridge helps people cross the river
the function of bridges is to give access to people and moving vehicles to places which beforehand were not avalible to access in the first place. eg to cross a river and get to the other side.
The Verrazano-Narrows Bridge is in New York, and it connects Staten Island and Brooklyn. It crosses over the Hudson River.
By a bridge
The Charles River in Massachusetts
It crosses the Saginaw River.
London Bridge crossed over the River Thames.
To cross a river
It crosses the St Lawrence river