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First years of wandering, 1576–1583

Bruno first went to the Genoese port of Noli, then to Savona, Turin and finally to Venice, where he published his lost work On the Signs of the Times with the permission (so he claimed at his trial) of the Dominican Remigio Nannini Fiorentino. From Venice he went to Padua, where he met fellow Dominicans who convinced him to wear his religious habit again. From Padua he went to Bergamo and then across the Alps to Chambéry and Lyon. His movements after this time are obscure.

In 1579, Bruno arrived in Geneva. During his Venetian trial, he told inquisitors that while in Geneva he told the Marchese de Vico of Naples, who was notable for helping Italian refugees in Geneva, "I did not intend to adopt the religion of the city. I desired to stay there only that I might live at liberty and in security." Bruno had a pair of breeches made for himself, and the Marchese and others apparently made Bruno a gift of a sword, hat, cape and other necessities for dressing himself; in such clothing Bruno could no longer be recognized as a priest. Things apparently went well for Bruno for a time, as he entered his name in the Rector's Book of the University of Geneva in May 1579. But in keeping with his personality he could not long remain silent. In August he published an attack on the work of Antoine de La Faye, a distinguished professor. Bruno and the printer, Jean Bergeon, were promptly arrested. Rather than apologizing, Bruno insisted on continuing to defend his publication. He was refused the right to take sacrament. Though this right was soon restored, he left Geneva.

He went to France, arriving first in Lyon, and thereafter settling for a time (1580–1581) in Toulouse, where he took his doctorate in theology and was elected by students to lecture in philosophy. He also attempted at this time to return to Catholicism, but was denied absolution by the Jesuit priest he approached. When religious strife broke out in the summer of 1581, he moved to Paris. There he held a cycle of thirty lectures on theological topics and also began to gain fame for his prodigious memory. His talents attracted the benevolent attention of the king Henry III; Bruno subsequently reported:

"I got me such a name that King Henry III summoned me one day to discover from me if the memory which I possessed was natural or acquired by magic art. I satisfied him that it did not come from sorcery but from organized knowledge; and, following this, I got a book on memory printed, entitled The Shadows of Ideas, which I dedicated to His Majesty. Forthwith he gave me an Extraordinary Lectureship with a salary."

In Paris, Bruno enjoyed the protection of his powerful French patrons. During this period, he published several works on mnemonics, including De umbris idearum (On the Shadows of Ideas, 1582), Ars memoriae (The Art of Memory, 1582), and Cantus circaeus (Circe's Song, 1582; described at Circe in the arts § Reasoning beasts). All of these were based on his mnemonic models of organized knowledge and experience, as opposed to the simplistic logic-based mnemonic techniques of Petrus Ramus then becoming popular. Bruno also published a comedy summarizing some of his philosophical positions, titled Il Candelaio (The Candlemaker, 1582). In the 16th century dedications were, as a rule, approved beforehand, and hence were a way of placing a work under the protection of an individual. Given that Bruno dedicated various works to the likes of King Henry III, Sir Philip Sidney, Michel de Castelnau (French Ambassador to England), and possibly Pope Pius V, it is apparent that this wanderer had risen sharply in status and moved in powerful circles.