Complex sentence: Formerly if the priest celebrated at a consecrated altar, the sacred elements were placed only on the eiliton, but in current practise the priest always uses the antimins even on a consecrated altar that has relics sealed in it.
Split into simpler sentences: Formerly if the priest celebrated at a consecrated altar, the sacred elements were placed only on the eiliton. However, in current practice the priest always uses the antimins, even on a consecrated altar that has relics sealed in it.