The former Cagliari defender has signed for the Giallorossi on an initial one-year loan deal.
"I'm happy to play for this club after six years at Cagliari and that's why I'd like to thank my former club," he told reporters at his official unveiling.
"I felt positive straight away - I knew a lot of the team from the national team or having played with them in the past.
"The media blew things out of proportion [with the Lazio move]. There was a deal between two clubs which didn't end in a transfer.
"Then Roma came in and I had no doubts at all.
"Had I already agreed terms with Lazio? You only talk terms once the two clubs have agreed a fee."
Astori is keen to work with Roma coach Rudi Garcia.
"A new adventure begins now - we have the squad to achieve our targets and I think we'll have a lot of fun.
"Garcia? He's someone who gives his players a lot and expects the same in return. He's a modern Coach.
"Being at Roma is a lot more appealing than playing for a lesser team."
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