Mesilla Plaza is the central plaza in the small town of Mesilla in far southern New Mexico. The plaza and a number of its surrounding buildings are a National Historic Landmark District, significant for its role in the transfers of power that brought first the original New Mexico Territory and later the Gadsden Purchase into United States control. The most notable building facing the plaza is the Basilica of San Albino, which has been on the plaza since its establishment in 1851.