The street commissioners who laid out the grid plan had assumed it would take several centuries for urban growth to reach 155th Street, where they ended the grid. “To have gone further might have furnished materials to the pernicious spirit of speculation,” they explained. Yet by the 1860s development was approaching 155th Street, requiring a new plan for the north end of the island, and by the end of the 19th century, the grid was fully laid out and filled in.