William Bianda has become Roma's ninth new signing of the summer, arriving from French second division club Lens.
Bianda follows Javier Pastore, Bryan Cristante, Antonio Mirante, Davide Santon, Nicolo Zaniolo, Ivan Marcano, Ante Coric and Justin Kluivert in joining last season's Champions League semifinalists.
The 18-year-old defender, who has made only five Ligue 2 appearances, was described as "an exciting prospect" by sporting director Monchi, who indicated that further new faces could arrive.
"He's been looked at in detail by our scouts," he told the club's website. "This is the kind of player I like to buy, because it's the result of the collaborative work of all the staff.
"He'll go straight into training with the first team, and it will be a big step up for him.
"We've bought nine players. I don't think there's a team in Italy, or Europe, that's done the same.
"All the talk is of sales, but Roma have only sold [Radja] Nainggolan, [Lukasz] Skorupski and [Marco] Tumminello. I'm happy with what we've done so far.
"My aim as a director of football has always been to try and provide the most ready squad possible to the coach, to let him get to work as soon as possible. Our plans for the season aren't done, but we've accomplished a large chunk of them.
"Roma, which was in difficulty this time last year, is now in good shape. I think these moments are worth enjoying fully."