With the summer already upon us, the rumour mill has gone into overdrive, and it surely promises to be another window of frenzied activity.In this article, however, we look back at the signings which had the most impact on their respective clubs in Serie A. From title-chasers to relegation dogfighters, there have been some really good business deals done by Italian sides in the 2019-20 season.Here are ten signings that have made the most impact in Serie A in the most recently-concluded season:Top 10 signings of Serie A's 2019-20 season#10 Ashley Young (Inter Milan)Ashley Young is enjoying the second winds of his career with Inter at 35!Inter Milan raided the Premier League in the recently-concluded season and bought as many as five players from the English shores. Ashley Young was one of the last players to arrive, joining Inter Milan in January this year, but finished as one of the best performers, especially after the restart.8 - Ashley Young (four goals, four assists) has been involved in 8+ goals in a single season in the top-5 European leagues for his first time since 2011/12, 13 with Manchester United. Rediscovery.#AtalantaInter pic.twitter.com/PeyY325GeE— OptaPaolo (@OptaPaolo) August 1, 2020The full-back looked like a man reborn, with his tireless sprints down the flank and his trademark cut-ins from the left turning back the calendar to the days when he used to be an absolute beast with Manchester United. He linked up very well with former Red Devils players Romelu Lukaku and Alexis Sanchez and was also involved in eight goals overall, six of which came post-lockdown.#9 Radja Nainggolan (Cagliari)Radja Nainggolan has had several issues off the field but none on itAn unconvincing spell with Inter Milan, coupled with his wife's illness as well as a fall-out with Antonio Conte, culminated with Radja Nainggolan returning to his "home" and joining the club where his "heart belongs".Upon arrival, the Belgian was once again at his rip-roaring self and posted some of his best numbers in years, scoring and assisting six times each. Under Nainggolan's leadership, Cagliari steered well clear of relegation, although they had to play without him in the last six Serie A games as he was ruled out with a calf injury.#8 Chris Smalling (AS Roma)Chris Smalling was back to his best in Serie A, and Manchester United have now recalled himDefence has perenially been AS Roma's Achilles heel and with 50+ goals conceded in Serie A in the recently-concluded season, the club went through the motions once again. The presence of Chris Smalling, however, proved to be a small consolation to their defensive woes.On loan from Manchester United, the Englishman was sound, composed and strong in the air. He also laid good quality passes and even contributed five goals. The 30-year-old star has established himself as one of the best players for Roma this season but unfortunately for them, he's set to return to the Old Trafford this week.