The U.S.S. Byzantium is a Federation starship in service to Starfleet in 2409. In that year, she led the U.S.S. Pollux and U.S.S. Sri Lanka against the Crystalline Entity, which was attacking a Federation colony in the Teneebia Sector.
Early in the battle, a fleet of Tholian starships forced the Byzantium on the defensive and bought time for the Entity to destroy the Pollox and the Sri Lanka. The Entity then fired a powerful Matter Conversion Beam, vaporizing 73 of the Byzantium's crew (including Captain Gorrus and half the bridge crew). The vessel's science officer managed to fire a sensor-scrambling probe that bought the ship enough time to escape the carnage and warp to safety.