The suspect was described as a 39-year-old legal resident from Ghana with several previous run-ins with the law. Authorities are evaluating what charges to press, a statement said.
Police said he broke into four churches in central Rome - twice on Friday evening and twice on Saturday morning - and damaged at least five religious statues.
A parish priest who witnessed one of the attacks, Father Pedro Savelli of Santa Prassede church, told the La Repubblica newspaper: "He was out of his mind, but luckily we made him run away before he also destroyed the cross."
"It was all over in a few seconds, and luckily not many people were in the church, no more than 15. But they were all terrified. That man was out of control, he said we were using sacred images in the wrong way and then hurled himself at the statues," Savelli added.