As the height of the Covid-19 pandemic conclusively proved, football is absolutely nothing without fans.
When supporters are not in stadiums to cheer the team through the good times and the bad times, games are a fraction of the spectacle that they should be.
Fans also have an enormous impact on proceedings. Why do you think stadiums like Anfield, the Santiago Bernabeu and Camp Nou are such fortresses, eh?
When home fans pack into the ground, they create an atmosphere that both motivates their own players and strikes fear into the opposition.
That's why clubs are desperate for their stadiums to be at capacity for each game, as it gives the team a huge advantage.
But which European teams have been the best at packing out their ground on matchday throughout the course of the 21st century?
LIVERPOOL, UNITED KINGDOM - MAY 01: Liverpool fans in the KOP End cheer prior to the UEFA Champions League semi final second leg match between Liverpool and Chelsea at Anfield on May 1, 2007 in Liverpool, England. (Photo by Clive Brunskill/Getty Images)
Thanks to PopFoot, we know the answers to that very question.
The stats-based Twitter account have provided the 40 European clubs with the highest average attendance since the turn of the millennium.
Check out their findings below...
BARCELONA, SPAIN - MARCH 08: FC Barcelona supporters wearing Lionel Messi shirts watch the game from the stands during the La Liga match between FC Barcelona and Rayo Vallecano de Madrid at Camp Nou on March 8, 2015 in Barcelona, Spain. (Photo by David Ramos/Getty Images)
The 40 European clubs with the highest average attendance in the 21st century
40. FC Nuremberg - 34,116
39. Napoli - 34,557
38. Aston Villa - 35,429
37. Athletic Bilbao - 36,228
36. Everton - 37,023
35. Hannover - 37,187
34. Sunderland - 37,516
33. West Ham United - 37,871
32. Lyon - 37,933
31. Werder Bremen - 38,526
BREMEN, GERMANY - MAY 15: A general view of SV Werder Bremen fans as they lift scarfs above their heads prior to kick off of the Second Bundesliga match between SV Werder Bremen and SSV Jahn Regensburg at Wohninvest Weserstadion on May 15, 2022 in Bremen, Germany. (Photo by Joosep Martinson/Getty Images)
30. Atletico Madrid - 39,015
29. Valencia - 39,286
28. Tottenham Hotspur - 39,288
27. Eintracht Frankfurt - 40,239
26. Benfica - 40,287
25. Chelsea - 40,871
24. Paris Saint-Germain - 41,238
23. AS Roma - 42,875
22. Feyenoord - 43,222
21. FC Cologne - 43,782
20. Borussia Monchengladbach - 44,250
19. Rangers - 44,933
18. Stuttgart - 45,384
17. Manchester City - 45,408
16. Liverpool - 45,526
15. Hertha Berlin - 46,452
14. Marseille - 47,915
13. Ajax - 48,175
12. Newcastle United - 50,424
11. AC Milan - 50,899
MILAN, ITALY - JANUARY 17: The supporters of Milan before the Serie A match between Milan and Siena at Stadio Giuseppe Meazza on January 17, 2010 in Milan, Italy. (Photo by Giuseppe Bellini/Getty Images)
10. Hamburg - 51,341
9. Celtic - 51,802
8. Inter Milan - 51,853
7. Arsenal - 53,372
6. FC Schalke - 60,456
5. Bayern Munich - 66,324
4. Barcelona - 68,864
3. Manchester United - 69,488
2. Real Madrid - 70,016
- Borussia Dortmund - 76,155
Dortmund and the famous 'Yellow Wall', you guys are just different gravy.
An average attendance of over 76,000 when the capacity is 81,365? Yeah, that is simply extraordinary.
Are Dortmund the best supported club in world football? Well, you can't really give a definitive answer to that question, but the numbers above are incredibly hard to ignore.
Elsewhere, United lead the way in terms of Premier League teams, while Real Madrid have the edge over Barcelona - as do Inter over their city rivals AC Milan.