in ecclesiastical antiquity, denotes an open place or court before a church, making part of what was called the narthex or antetemple.

The atrium in the ancient churches was a large area or square plat of ground, surrounded with a portico or cloister, situate between the porch or vestibule of the church, and the body of the church.

Some have mistakenly confounded the atrium with the porch or vestibule, from which it was distinct; others with the narthex, of which it was only a part.

The atrium was the mansion of those who were not suffered to enter farther into the church. More particularly, it was the place where the first class of penitents stood to beg the prayers of the faithful as they went into the church.

Atrium is also used, in the canon law, for the cemetery or church-yard. In this sense we find a law prohibiting buildings to be raised in atrio ecclesiae, except for the clergy; which the glossary explains thus, id est in cimiterio, which includes the space of forty paces around a large church, or thirty round a little church or chapel.