12. There was a Marsh in Harlem

Commissioner's Plan 1811-Map-NYC-Library of Congress-008

These days it can be hard to remember that Manhattan was once full of streams and marshes that protected the coast from flooding. The grid rather bypassed the Harlem Marsh when it was created, but has since been filled in. The commissioners smartly numbered the streets as if there were numbers there, so it jumped from 103 to 110 in this area.