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.Germany's oldest episcopal church is a combination of a whopping 1,700 years of building, art and religious history. This can be seen in the architecture as well as inside the cathedral, where the cathedral pulpit, the scallop shell-shaped baptismal font in the western chancel and the imposing design of the eastern chancel with the pilgrims' staircase and the view of the Baroque chapel for the relic of the Seamless Robe of Jesus captivate visitors. A number of bishops' gravestones also bear witness to the church's long history.The Holy Door, which connects the cathedral and the Church of Our Lady, is another of the cathedral's main attractions. It was opened in 2015 for the Holy Year of Mercy, one of the major moments when the past can be at one with the present.