Tuesday's deadline day marked the end of a truly remarkable <a href="https://www.thenationalnews.com/sport/football/2021/09/01/ronaldo-kean-and-lukaku-find-way-back-home-in-summer-of-transfer-coups/" target="_blank">summer transfer window</a>, which saw the two greatest players of their generation make sensational moves and a number of expensive deals take place. <a href="https://www.thenationalnews.com/sport/football/2021/08/31/psg-must-find-way-of-weaving-talents-of-messi-neymar-and-co-into-balanced-team/" target="_blank">Lionel Messi</a> did the seemingly unimaginable by leaving Barcelona after 17 years having failed to agree a new contract amid the club's crippling financial problems. The Argentine soon pitched up at Paris Saint-Germain, amid much fanfare, where <a href="https://www.thenationalnews.com/sport/2021/08/10/lionel-messi-agrees-two-year-deal-with-psg-report/" target="_blank">he signed a two-year contract</a> with the option of a third. Messi's great rival <a href="https://www.thenationalnews.com/sport/football/2021/08/31/cristiano-ronaldo-overwhelmed-as-manchester-united-complete-signing-on-two-year-deal/" target="_blank">Cristiano Ronaldo</a> later followed suit by sealing a stunning move of his own as the Portuguese superstar <a href="https://www.thenationalnews.com/sport/football/2021/08/31/cristiano-ronaldo-overwhelmed-as-manchester-united-complete-signing-on-two-year-deal/" target="_blank">returned to Manchester United</a> 12 years after leaving the Premier League club. Aside from those two spectacular deals, plenty of money was exchanged between clubs this summer. Jack Grealish's <a href="https://www.thenationalnews.com/sport/football/2021/08/05/manchester-city-sign-aston-villas-jack-grealish-for-british-record-fee/" target="_blank">British record move</a> from Aston Villa to Manchester City represented the biggest deal of the window, closely followed by <a href="https://www.thenationalnews.com/sport/football/2021/08/12/romelu-lukaku-rejoins-chelsea-in-975m-deal-from-inter-milan/" target="_blank">Romelu Lukaku's return to Chelsea</a> from Inter Milan. In addition to Ronaldo, Manchester United were responsible for two of the top five biggest transfers of the window, with Jadon Sancho arriving from Borussia Dortmund and Raphael Varane making the move from Real Madrid. With the summer transfer window now closed, the photo gallery above details the 50 biggest deals of the off-season. All figures are sourced from <a href="https://www.transfermarkt.com/" target="_blank">transfermarkt.com</a> and the rankings are based on transfer fee or the player's market value, whichever is greater. To move on to the next photo, click on the arrows or if using a mobile device, simply swipe. 1. Jack Grealish - Aston Villa to Manchester City (transfer fee - €117.5m / market value - €65.00m) 2. Romelu Lukaku - Inter Milan to Chelsea (transfer fee - €115m / market value - €100m) 3. Jadon Sancho - Borussia Dortmund to Manchester United (transfer fee - €85m / market value - €100m) 4. Lionel Messi - Barcelona to Paris Saint-Germain (transfer fee - free / market value - €80m) 5. Raphael Varane - Real Madrid to Manchester United (transfer fee - €40m / market value - €70m) 6. Achraf Hakimi - Inter Milan to Paris Saint-Germain (transfer fee - €60m / market value - €60m) 7. Dayot Upamecano - RB Leipzig to Bayern Munich (transfer fee - €42.5m / market value - €60m) 8. Gianluigi Donnarumma - AC Milan to Paris Saint-Germain (transfer fee - free / market value - €60m) 9. Antoine Griezmann - Barcelona to Atletico Madrid (transfer fee - loan / market value - €60m) 10. Ben White - Brighton to Arsenal (transfer fee - €58.5m / market value - €28m) <br/>