Trier Cathedral, the oldest bishop’s church in Germany, stands today in Trier’s center above a former palace from the era of the Roman Emperor Constantine the Great. The palace complex was supplanted in the 4th century by the largest Christian church complex from ancient times. It consisted of four basilicas joined by a large baptistry; the complex covered an area extending to the present Main Market. Tours under the building of the Cathedral Information show the remains of the first Early Christian assembly room north of the Alps from the late 3rd century and the remains of the first basilica.