The Eastern Parkway Line to Atlantic Avenue is part of Contract 2 of the Interborough Rapid Transit Company's plan to construct an extension of the original subway, Contract 1. Contract 2 extended the original line from City Hall in Manhattan to Atlantic Avenue in Brooklyn, and the contract was signed on September 11, 1902.
https://en.wikipedia.org/wiki/IRT_Eastern_Parkway_Line#History 9-11
