 In 1543, Nicolaus Copernicus had already posited that the planets orbited the Sun as the Earth does; combined, these two concepts led to the thought that the planets might be "worlds" similar to the Earth.Public expression of such concepts could be dangerous, however; Giordano Bruno was martyred in 1600 for, among other things, imagining an infinite number of other worlds, and claiming that "Innumerable suns exist; innumerable Earths revolve about these suns ...Living beings inhabit these worlds" in "De l'infinito universo e mondi" ("Concerning the Infinite Universe and Worlds", 1584).