The city of Arona, on the Piedmontese shore of Lake Maggiore in the diocese and province of Novara, celebrates two groups of martyrs as its patron saints: Felinus and Gratian, and Carpophorus and Fidelis. Still today, they are the central figures of the traditional feast of the Tredicino that is celebrated in March of each year on the shores of the lake. The origin of the feast, which of course is celebrated on the 13th of the month (hence the name Tredicino - i.e. the thirteenth) is linked to the presence in Arona of the relics of the four saints. To understand the reason for which this anniversary is so important and to shed light on the identity of these holy martyrs, we must necessarily start from information contained in a document, still preserved in the parish archives, the oldest parts of which date back to the 10th century. The manuscript consists of 249 sheets of parchment is written in medieval Latin, using Gothic script. Among the many facts, there is also a narration of the Passion of Saints Gratianinus or Gratian and Felinus and of the transfer of their relics to Arona. According to the story, Gratian and Felinus were two Roman soldiers stationed in Perugia, who were converted to Christianity by the bishop of the city, by whom they were also baptized. It appears that they were martyred during the persecution of the emperor Decius, together with other Christians, for not wanting to renounce their faith. Their bodies were buried in a place not far from where they were martyred. In 979, the count of Seprio, Amitto, a captain under Emperor Otto I, transferred, with the permission of the bishop, the relics of the two saints to Arona, as a gift to the new monastery that was being built and would later be dedicated to them. The establishment of the coenoby by Amitto was seen as a form of penance for the excommunication he had been administered, since his soldiers had set fire to the portico of the Basilica of St. Paul on the Via Ostiense. Hagiographic critics tend to consider the story of the two martyrs of Perugia a legend which, according to some experts, should be identified as Gratilianus and Felicissima. If this assumption is true, it is certain however that at the time of Amitto confusion was made between the two pairs of saints, perhaps due to the misreading or incorrect transcription of Gratilianus into Gratinianus and the abbreviation Fel. interpreted as Felinus instead of Felicissima. Even greater problems arise when trying to identify the other two martyrs: Carpophorus and Fidelis, news of whom is provided by father Francescantonio Zaccaria, an 18th century Jesuit who researched and studied many documents contained in the archives of Arona. He remembers the local tradition which said that the remains of the two saints, also Roman soldiers belonging to the famous Theban Legion, were transferred to the city by a cleric of the monastery, perhaps to save them from pillaging at the time of one of the wars fought between Milan and Como. However, the latter has always challenged Arona for the possession of the remains of St. Fidelis, jealously preserved in the local church that bears his name. The martyrdom of the saint did, in fact, occur on the northern shore of Lake Lario (also known as Lake Como), near Samolaco, where he was found by imperial soldiers ordered to kill him. His body, which was initially placed in a sepulcher above which a church was built, was transported to Como in 964. Throughout the centuries there has been much evidence supporting the presence in this city of the saint's relics, the most important of which concern the recognition they were subject to by the local bishops. One took place in 1365, approximately fifteen years after the presumed transfer to Arona (which bishop Carlo Bascapè places in 1350) while another occurred in 1638. For the first one, the bishop Stefano Gatti had engraved on the box that contained the holy remains “Here lies the entire and intact body of the martyr Fidelis,” almost as if in response to the claims of the city of the area of Verbania. Here, however, many documents dating back to 1259 and 1321 attest the existence of veneration in Arona for this saint and his companion, Carpophorus, of whom it claims to possess the holy bodies. Further support in favor of the city of Arona seems to come from the writings of Goffredo da Bussero (ca. 1220 – 1289) who, discussing a group of presumed Theban Legion martyrs killed in Lombard territories, states "sed horum duo corpora ad monasterium de Arona dati sunt” - but these two bodies have been given to the monastery of the Arona. However, the author does not specify whose remains were given among those of saints Fidelis, Carpophorus, Cassius, Exanthus, Licinius, Severus and Secundus. In 1576, St. Charles Borromeo gave orders to transfer to Milan the bones of Saints Carpophorus and Fidelis found, nearly a century earlier (1487), in a wall of the abbey church while working on the building. His intention was to place them in the Milanese church that was being built in their name. Though the people of Arona were not particularly devoted to these two saints, the news that their relics would be removed from the city were enough to give rise to a protest that was as intense as it was unexpected. The city authorities, under popular pressure, spoke to Borromeo, finally reaching a compromise with which it was decided that the two left forearms of the martyrs were to be returned to Arona. The restitution took place on March 13th of the same year, marked by a grand popular feast that the chronicles of the time describe as memorable, with the participation of thirty, perhaps forty thousand people coming from all the towns along the lake's shore. The city council decreed that each year the anniversary of this event would be a holiday and authorized the holding of a fair which, with the passing of the years, grew more and more, attracting thousands of people to the lake. The memory of the restitution is also joined by the commemoration for the other two martyrs Gratianus and Felinus, celebrating them all on the same day, which was once the third Sunday after Pentecost. Regardless of the biographical events of the four martyrs, the problem of identifying their relics still remains unsolved. We can assume that as far as Gratianus and Felinus are concerned, only a part of the remains of the two martyrs arrived from Umbria which, if identified with Gratilianus and Felicissima, still rest in the cathedral of Civita Castellana and in the Church of St. Sixtus in Viterbo, respectively. As for Carpophorus and Fidelis, the doubt remains, if credit is given to the news of their transfer, regarding which bodies were transferred to Arona, being that even in the case of St. Fidelis, the people of Como venerate his relics in the now parish church of St. Brigit in the hamlet of Camerata, where they were transferred, in 1932, from the nearby Romanesque basilica erected in her honor. Only accurate recognition, combined with a scientific and anatomical investigation and a comparison with the depositories of Como, could help shed light on the origin and identification of the relics of Arona. The remains of Saints Gratinianus and Felinus are preserved, since the 1700s, in a small chapel above the main altar, while the two forearms of Saints Carpophorus and Fidelis, returned by Borromeo, are housed in a small shrine on the altar of the second chapel on the right. In local art, the four saints are portrayed in Renaissance military attire, without specific details distinguishing them. The most important examples are of course preserved in the church dedicated to them in Arona. In particular we must mention the 15th century altar-piece, belonging to the abbot Calagrani, and made by Ambrogio Bergognone (1489), placed on the wall of the choir behind the altar and the marble reliefs to the sides of the main altar, probably by the sculptor Pollicetus de Luonibus of Milan.