Still standing from this era are the Porta Nigra, a massive Roman gate and fortification, the Amphitheater, and three thermal baths. A Rome Ticket (Eintrittspreise Kombiticket) gets you into all the Roman attractions for 6.20. You can buy it at the Tourist Information office at the Porta Nigra.
The Roman antiquities are best seen during the off-season, because by the middle of June they are being prepared for the outdoor performance season, with all the modern metalwork that implies.
The pictures in this series show views of the antiquities with the "modern" city of Trier showing through.