The so-called Basilica, Constantine's throne room, is the largest surviving single-room structure from Roman times.

The Romans wanted the architecture to express the magnificence and might of the emperor. The size is amazing even by today's standards: 27 m (90 ft) wide, 33 m (108 ft) high, and 67 m (220 ft) long - with an adjoining hall outside even 75 m (250 ft). This depth is magnified by an optical illusion - both the windows of the apse as well as the niches underneath become progressively smaller towards the middle, thus enhancing the impression of length.

The Roman building was embellished by colorful marble inlay, mosaics, and statues and was made comfortable by a hollow-floor heating system, but all this splendor and technology were destroyed (in the 5th century) by the Germanic Franks, who built a settlement inside the roofless ruin.

Later on, the archbishop used it as his administrative center and it was enlarged by three palace wings after 1614. Since the middle of the 19th century, it has been used as the first and oldest Protestant church in Catholic Trier with a splendid organ answered by a seven-second echo.

Open:
April - October: Monday - Saturday 10 a.m. - 6 p.m., Sunday 12 noon - 6 p.m. November - March: Tuesday - Saturday 11 a.m. - 12 noon and 3 p.m. - 4 p.m., Sunday 12 noon - 1 p.m.,  Monday closed


Note:
During the services and concerts it is not possible to visit the Basilica.
Cost: There is no admission charge for the Basilica - except for concerts.