Not one of these roads was blocked up by the wall of Aurelian, and wherever gates were made in the latter, they received their names from the streets into which they led. Thus we find the Porta Flaminia, Porta Pinciana (a secondary gate near the Collina, leading probably to a less important way, not a high-road, a gate being necessary for the palace), P. Salaria, P. Nomentana, and then two Portae Tiburtinae, because there were two roads leading to Tibur; one of these gates seems to have had no particular name of its own, though it may have been called P. Valeria. Next came the P. Praenestina and Labicana, both in one building, though distinct; P. Metronia (probably named after a palace), P. Latina, P. Asinaria (P. S. Giovanni), P. Appia, P. Ardeatina, P. Ostiensis, beyond the river P. Portuensis, P. Septimiana or Aurelia, between the Janiculus and the river, probably named after the Thermae of Septimius Severus; and at the bridge (Pons Aelius) the P. Aelia. With the exception of the Pincia and Metronia, you still find almost the same gates leading to the same roads. This circumference of Rome is mentioned by Procopius in his account of the siege of the city. In the sixth century a change took place in the nomenclature, many gates receiving new names from the nearest important churches: thus the P. Asinaria was at a very early date called P. S. Giovanni; the P. Appia, P. S. Sebastiani, from a basilica; the P. Ostiensis, S. Pauli; P. Aurelia, S. Pancratii; the P. S. Lorenzo (Praenestina) also received its name from the basilica S. Laurentii. The P. Salaria and Nomentana retained their names until the sixteenth century.