One part horse race, one part religious pilgrimage, this dangerous yearly race is run by brave horsemen atop their faithful steeds, re-enacting the victory of Emperor Constantine, or "Costantino il Grande", over his rival Maxentius in the year 312 in Rome.

Caesar Flavius Valerius Aurelius Constantinus Augustus, AKA Constantine I, was born is what is now Nis, Serbia, and rose though military ranks in the Roman army before following in his father's footsteps as a co-emperor in 306 AD, part of the second generation tetrarchy (wherein 4 co-emperors managed the far flung Roman Empire). He rose to power in the midst of the Diocletian "Great Persecutions" of the then outlawed Christians.

The tetrarchy fell apart in the wake of the Emperor Galerius' death, with the remaining co-emperors and their heirs scrabbling for power. In the summer of 311, Constantine's brother in law and semi-legitimate co-emperor Maxentius declared war on Constantine from Rome. In the spring of the following year, Constantine moved 40,000 men south across the alps into Italy, headed for Rome, approaching the city on Via Flaminia. As he led his men into battle, he saw a vision of a flaming cross in the sky inscribed with the words In Hoc Signo Vinces or "In this sign, you will conquer."

In the Battle of the Milvian Bridge, Constantine's forces obliterated those of Maxentius, and rode into Rome in victory. His triumph under the sign of the cross paved the way for his Edict of Milan in 313, which effectively ended the persecutions of Christians in Rome. The bridge where the battle took place still stands in Rome, although a bit changed by time, and the battle scene was famously captured in a huge fresco in the Vatican's Sala di Costantino ("Hall of Constantine").

Every year in July participants in L'Ardia di San Costantino Festival include riders representing Constantine and the Maxentius, costumed flag men and a fairly believable army doing their best to thwart the efforts of Maxentius. The roles are played by villagers who wait years, even decades, for the privilege. The end is still always a surprise.

The faithful make pilgrimages to Sedilo from all over Sardinia. Constantine's victory means Christianity's survival for another year.