Underground basilica of Porta Maggiore

The Porta Maggiore Basilica is an underground basilica discovered in 1917 near Porta Maggiore in Rome. It is dated to the 1st century BC. It is believed to have been the meeting place of the neo-Pythagoreans and is the only historical site that has been associated with the neo-Pythagorean movement. This school of mystical Hellenistic philosophy preached asceticism and was based on the works of Pythagoras and Plato. It was a precursor to the basilicas built during the Christian period, centuries later. It was opened to small groups of visitors in April 2015.

Archaeological site data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).