Trier was founded by the Romans no later than 16 B.C.; it eventually became the capital of the Roman province of Gallia Belgica. It is the oldest city in Germany and the oldest seat of a Christian bishop north of the Alps. The Porta Nigra (Black Gate) in Trier is the best preserved Roman city gate north of the Alps. It was built between A.D. 186 and 200 and guarded the northern entrance to the city. After 1035, the Porta Nigra was converted into a church. During the Napoleonic Wars – when Trier was occupied by the French – Napoleon ordered the Porta Nigra to be restored back to its Roman form.