During the Klingon Civil War, Starfleet blockaded the border in an attempt to expose suspected Romulan covert support of the House of Duras. (TNG: "Redemption", "Redemption II") In 2370, the Romulan vessel Imparatex disappeared while on a routine patrol of the border. (Ship Recognition Manual, Volume 5: Starships of the Romulan Star Empire)