The so-called ‘Neo-Pythagorean Basilica’ at Porta Maggiore in Rome is one of the most famous and most discussed hypogeal monuments in Rome. It was certainly in use for a short time during the first half of the first century AD, but its purpose is still far from clear. The most probable interpretation is that it was a temple dedicated to Neo-Pythagorean cults. We describe here the preliminary results of a detailed archaeoastronomical study of the Basilica undertaken in order to contribute to the understanding of the role of this fascinating monument.