The Emperor Phocas (602-610) is not one of the better known Emperors; he was the Emperor before Heraclius, the one who trounced the Persians and so exhausted both the Empire and the Persian Empire in the process that the Islamic hordes simply mopped up most of both within a very few years. Back to Phocas. Oddly enough he is better known in Rome, where his column still stands in the forum, and also for another interesting act which we are celebrating today.
The Pantheon is one of the most remarkable buildings in Rome. Originally built (according to the inscription on the front) in 27bc by Marcus Agrippa, the friend of Augustus, it was radically altered by Hadrian in about 125ad, the cella being a drum surmounted by a concrete dome, the largest in the world at that time, and not surpassed until relatively modern times. It was dedicated to all the gods, and the various niches inside presumably held their statues; the marble decoration still to be seen there is original, and so this is one of the very few real ancient Roman buildings one can really walk into and around.
Now here comes the point. By the time of Phocas, the ancient pagan religion had been outlawed for some time. Phocas himself was particularly beastly to people who tried to worship the old gods even in secret. He gave permission to Pope St Boniface IV (whose feast we celebrated yesterday) for the Pantheon to be converted into a church. Boniface did so, and brought the bodies of many people (especially the martyrs) from the old catacombs and reburied them inside the Pantheon—the Catacombs, being outside the city walls, were no longer considered safe, on account of the various barbarian (and soon Islamic) raids. And so the Pantheon was consecrated the church of St Maria ad Martyres, which remains its official title to this day, on 9th May 609, which is to say 1400 years ago today.
On another topic, if you visit the Pantheon, do not miss the caffe granita at the little cafe called the Tazza d'Oro on the edge of the Pantheon square.
Here's a Mass celebrated on the feast itself; shame there were so few there to enjoy it, but a note on the New Liturgical Movement blog mentions that it was arranged a mere two days beforehand, celebrated during the siesta and while there was a major procession of the Bd. Sacrament at the Angelicum.