Dhiammara

Bearing the Staff of Earth and the Harp of Winds, the Lady Aurian secretly returns to the holy city of Nexis--ten years in the future. Now its marbled towers are desolate, its river port ravaged, its magefolk a mere legend. Here she must begin the search for her vanished soulmate, Anvar, and her lost child...and hunt down the evil adversary who stole from her the Sword of Flame, last of the four great primal weapons. But Aurian's final battle awaits her far away in the southlands. For there dwells her old nemesis, the crazed Archmage Miathan--and there, in the ancient city of Dhiammara, broods a dark magic that could shatter forever the destined redemption of her world.

This is #4 in The Aurian Saga.