"The ceremony was truly unique and Mena looked breathtaking," a guest tells PEOPLE. "They are very much in love."
The two, who have been engaged since 2008, planned a private reception following their ceremony.
Suvari, 31, and Sestito, 25, met at the Toronto Film Festival in 2007. The couple chose Rome as their wedding locale because most of Sestito's family lives near the city.
"We just understood each other," Sestito told PEOPLE in 2008. "She's very caring and understanding. There was a connection."
Suvari will next be seen in the comedy, You May Not Kiss The Bride, costarring Dave Annable.