Torre di Mariano II, Medieval tower in Piazza Roma, Oristano, Italy

Torre di Mariano II is a medieval tower in Piazza Roma, northern Oristano, built of sandstone bricks from Tharros laid in rusticated blocks up to about seven metres, with a granite base below. It has three overlapping wooden floors and rises about 19 metres; a small crenellated turret on top brings the total height to 28 metres.

Built in 1290 by Judge Mariano II of Arborea, the tower was the northern gate of Oristano's medieval walls. It was one of four main towers, alongside Portixedda, San Filippo and San Marco. Porta Mari, its twin to the south, was demolished in the early 1900s; San Filippo collapsed in 1872. In 1377 and 1378 ambassadors of Duke Louis I of Anjou passed through Porta Mari.

In Sardinian the tower is called Porta Ponti, "bridge gate", after the nearby Roman bridge over the Tirso, and Porta Manna, "great gate", because it was larger than the other twenty-eight watchtowers of the walls. It also bore the name of Saint Christopher, whose Spanish retablo it housed.

The tower stands in central Oristano near Piazza Roma and is visible from outside at any time since it occupies a central location. Visitors can view the exterior and structure throughout the year.

The tower's name in Sardinian, Porta Manna ("great gate"), refers to its size relative to the other twenty-eight watchtowers of Oristano's medieval walls. Only it and the Torre di Portixedda survive of the four main towers; Porta Mari was demolished in the early 1900s and the Torre di San Filippo collapsed in 1872.