Hieron. Ep. ad Evagrium.
Et ut sciamus traditiones Apostolicas sumptas de veteri Testamento, quod Aaron & filii ejus at{que} Levitae in Templo fuerint, hoc sibi E∣piscopi Presbyteri & Diaconi in ecclesia.
Here he compares Aaron and his two Sons to the Evangelist, Pa∣stor and Teacher (though I suppose the true order was broken before Hieroms time) and the Levites to the Deacons.
Gregory is forced to confess the truth, though, as it were, against his will, 16 Hom. super Ezek. lib. 2. p. 72. Orientalis via tres hinc & tres inde Thalamos habere memoratur: non inconvenienter acci∣pimus, si tres esse fidelium ordines.
Now as there are three Orders of Believers, so there were three Chambers or Meeting-places to meet in, and Ministery implyed, though then at Rome were no such Order.