Burned at the stake for heresy in Rome in 1600, the Italian philosopher Giordano Bruno was the first modern thinker to propose that the universe contained an infinite number of planetary systems revolving around individual stars. He announced his startling propositions at the moment when European explorers were beginning to reveal the real size and complexity of earth itself (indeed, Bruno also spoke forcefully against the violence and profiteering of Spanish colonial efforts) and when natural philosophers had begun to dispute about the very structure of the universe. It may not be a coincidence that the religious troubles of sixteenth–century Europe arose at a time when humanity’s very place in the world and the cosmos no longer seemed certain. In Bruno’s case, pursuit of his ideas compelled him to leave behind not only the security of his Dominican convent in Naples, but also, and more radically, the security of a traditional sense of who and where he was. His infinite universe terrified a thinker as unconventional as Johannes Kepler, and still more it terrified the Inquisition. For Bruno himself, the excitement of this infinitely expanded vision of the cosmos was usually enough to overrule any doubt, but when Kepler compared living in Bruno’s universe to permanent exile, he captured an essential quality of the Italian philosopher: an intense solitude, a solitude for which his philosophy was only ever a partial cure.