Oak Trees used in bridge building date the city to 17BC. The city wall was 8m high by 3m wide. Porta Negra was one of the City Gates. Later St Simon lived in Porta Negra and after he died it was extended upwards to become a church to celebrate him. In Napoleonic times Trier had more churches than Paris or London and Napoleon tore down many churches but left the Porta Negra believing it to be an early Gallic Fort. In Roman times Trier was one of the most important cities of the Roman Empire and one of largest in the world.