Lewis & Short

Trājānus, i, m., Trajan, a Roman emperor, who reigned A.D. 98-118, proverbial for his justice and benevolence: Augusto felicior, Trajano melior, Eutr. 8, 5.
Hence, Trājānus, a, um, adj., of or belonging to Trajan: aqua, Front. Aquaed. 93: VIA, the Appian Way, restored by Trajan, Inscr. Grut. 199, 1.