He was arrested in Venice, and confined in the Piombi for six years, without books, or paper, or friends.
In England he had given lectures on the plurality of worlds, and in that country had written, in Italian, his most important works.

It added not a little to the exasperation against him, that he was perpetually declaiming against the insincerity; the impostures, of his persecutors--that wherever he went he found skepticism varnished over and concealed by hypocrisy; and that it was not against the belief of men, but against their pretended belief, that he was fighting; that he was struggling with an orthodoxy that had neither morality nor faith.
In his "Evening Conversations" he had insisted that the Scriptures were never intended to teach science, but morals only; and that they cannot be received as of any authority on astronomical and physical subjects.
Especially must we reject the view they reveal to us of the constitution of the world, that the earth is a flat surface, supported on pillars; that the sky is a firmament--the floor of heaven.

On the contrary, we must believe that the universe is infinite, and that it is filled with self-luminous and opaque worlds, many of them inhabited; that there is nothing above and around us but space and stars.

His meditations on these subjects had brought him to the conclusion that the views of Averroes are not far from the truth--that there is an Intellect which animates the universe, and of this Intellect the visible world is only an emanation or manifestation, originated and sustained by force derived from it, and, were that force withdrawn, all things would disappear.
This ever-present, all-pervading Intellect is God, who lives in all things, even such as seem not to live; that every thing is ready to become organized, to burst into life.

God is, therefore, "the One Sole Cause of Things," "the All in All." Bruno may hence be considered among philosophical writers as intermediate between Averroes and Spinoza.