Some 500 Black Lives Matter protesters marched onto the roadway of the Brooklyn Bridge Friday night — where they sat down and blocked traffic for about an hour before moving on.

The protesters had gathered at the Barclays Center before taking the bridge.

The group wound up retreating back to Brooklyn about an hour later after a large number of cops massed on the Manhattan side of the bridge and began moving toward them.

No arrests were made, a police spokesman said.