Roma have signed Amadou Diawara from Napoli for €21 million (£19m, $24m), who becomes Paulo Fonseca's third signing of the summer.
The midfielder, on international duty with Guinea at the Africa Cup of Nations, has signed a five-year deal.
"We have been following Amadou for a while now," said Roma's chief executive Guido Fienga.
"He is a player whose talent has been clear to those in Italy for a number of years.
"We are pleased to welcome him to Roma, with the confidence that he can become an important player for the club."
Roma announced the deal coupled with a social media video raising awareness of missing children.
Official: Amadou Diawara is now a Roma player.— AS Roma English (@ASRomaEN) July 1, 2019
This summer #ASRoma is using the publicity generated by each transfer announcement video on social media to help raise awareness about the search for missing children globally.
@MissingKids @telefonoazzurro pic.twitter.com/bz1eCyRm9F
Fonseca's squad is taking shape after the coach was brought in from Shakhtar Donetsk to replace Claudio Ranieri.
Roma signed Italy international Leonardo Spinazzola for a fee of €29.5m ($33m, £26m) on Sunday, with the left-back joining from Juventus, while 20-year-old defender Luca Pellegrini signed for the Serie A champions for €22 million (£20m, $25m).
Edin Dzeko has been linked with a switch to Inter, though, while rumours suggesting Roma could sign Gonzalo Higuain from Juve have been denied by the striker's agent and brother.
Nicolo Barella is also said to be a target for Roma, with reports claiming they are set to beat Inter to the signature of the Cagliari midfielder.
Manolas, meanwhile, has posted a farewell message to Roma on social media.
"I want to thank the coaches, team-mates and all the fans who have stood by me and supported me over the years," the Greece centre-back wrote on Instagram.
"I spent five wonderful years, I always gave everything with love for this team."