The Second Siege of Minas Ithil was an engagement between the armies of Gondor and Mordor during the War of the Last Alliance. The Gondorian host, commanded by Anárion, brother of Isildur, counterattacked the citadel after it had fallen a year before, defeating Mordor's garrison and recapturing Minas Ithil.
In SA 3429, Isildur, who was then in command of Minas Ithil, lost the citadel to a large army that had marched from Mordor's interior. Though he managed to escape with his family, Mordor's hosts now were poised to assault the Anduin, and caused terror and bloodshed for the forces of Gondor in Ithilien. A year after Minas Ithil fell, Anárion led an army from Osgiliath in an attempt to take the fortress. In less than a year, they were victorious.
The reconquest of Minas Ithil helped to prevent a Mordor assault from being launched across the Anduin unopposed, and allowed the Last Alliance to concentrate on a single front of war, far to the north. Anárion rebuilt Minas Ithil, but in the Third Age it fell into near-abandonment by Gondor, only to be retaken by the Ringwraiths in TA 2002.