When the Relic weapons were introduced in 1.22b this seems to be the info given on Curtana:
Long has the sacred sword Oathkeeper been bestowed upon the commander of the Sultansworn, vowed protectors of Ul’dah’s ruler. Yet it is not alone in its greatness. At the time of its making, three other swords were struck from the same ore and forged in the same fires. These brethren blades, Curtana among them, were then gifted to the three noble paladins by whose hand the brotherhood of the Sultansworn was founded. * Curtana and the Holy Shield are a set, and are awarded together.
Also, if I remember right, Oathkeeper is still missing and has yet to be shown in game. As for the sword used by the Roe Paladin in the Paladin job quests, Curtana, Thyrus and the Artemis Bow are all supposed to be unique weapons, but one NPC in each job story is seen wielding a weapon that looks identical to the lost Relics.