In 2152 Enterprise blundered into a cloaked Romulan minefield, giving humans their first direct encounter with the Romulan Star Empire, though no Romulan was ever seen.
While approaching an uncharted planet, Enterprise struck an invisible mine, and a second one attached itself to the hull. Malcolm Reed went outside to disarm it and was pinned in place when the mine extended a spike through his leg.
A cloaked Romulan ship appeared and ordered Enterprise out of what it claimed as its territory. Archer and Reed finally cut the mine loose along with a section of hull plating. The encounter left Starfleet with only the barest knowledge of the Romulans, a mystery that lasted through the war that followed.