San Giulio was born in 330 AD on the Greek island of Aegina. He had a brother, San Giuliano, who accompanied him during travels worldwide. After conflicts with pagans opposing Christians and disputes with early Christians over doctrinal interpretation, he departed Aegina for Italy.
During his Italian pilgrimage, he received imperial authorization to demolish pagan temples and construct Christian churches atop them. Upon reaching Lake Orta's region, he became captivated by an island's isolated beauty and resolved to build a church honoring Christ there.
Requesting transport by boat to the island, he encountered resistance—local inhabitants refused, claiming it harbored dragons, serpents, and dangerous giant creatures. San Giulio then performed his first miracle: spreading his cloak across the water, stepping onto it, and commanding it to carry him safely to the island.
Upon arrival, he drove away the island's monsters. Evidence allegedly remains—"a very large vertebra of a frightening creature" hangs suspended in the Church of San Giulio's sacristy by cord.
San Giulio began constructing his church, reportedly the hundredth he and his brother would build. Historians debate whether two distinct brothers existed or if San Giulio was called by different names throughout history. San Giuliano's body supposedly rested on the island before transfer to Gozzano, while San Giulio's remains rest in a crypt beneath the church altar, accessible to visitors.
The island adopted San Giulio's name following his church's establishment. He secured Christian Church possession through the Bishops of Novara, placing it under the Novarese Curia's protection.