Scientists have mapped the largest coral reef deep in the ocean, stretching hundreds of miles off the U.S. Atlantic coast.

While researchers have known since the 1960s that some coral were present off the Atlantic, the reef’s size remained a mystery until new underwater mapping technology made it possible to construct 3D images of the ocean floor.

The largest yet known deep coral reef “has been right under our noses, waiting to be discovered,” said Derek Sowers, an oceanographer at the nonprofit Ocean Exploration Trust.

Sowers and other scientists, including several at the National Oceanic and Atmospheric Administration, recently published maps of the reef in the journal Geomatics.