The Federation-Gorn border was the spared border between the United Federation of Planets and the Gorn Hegemony. The Metron Consortium lay beyond the Federation-Gorn border in the 23rd century. (TOS: "Arena")
The USS Valorous was assigned for three years patrolling the border in the first decade of the 24th century. (Ship Recognition Manual, Volume 4: Starships of the Original Series Era)