There were several variations of the basic plan of the secular basilica, always some kind of rectangular hall, but the one usually followed for churches had a central nave with one aisle at each side and an apse at one end opposite to the main door at the other end. In (and often also in front of) the apse was a raised platform, where the altar was placed, and from where the clergy officiated. In secular building this plan was more typically used for the smaller audience halls of the emperors, governors, and the very rich than for the great public basilicas functioning as law courts and other public purposes. Constantine built a basilica of this type in his palace complex at Trier, later very easily adopted for use as a church. It is a long rectangle two storeys high, with ranks of arch-headed windows one above the other, without aisles (there was no mercantile exchange in this imperial basilica) and, at the far end beyond a huge arch, the apse in which Constantine held state.