Inter Milan players were so excited by clinching the Italian title that they took an impromptu open top bus to the city centre in the early hours of Sunday morning.
AC Milan's 2-1 defeat at Udinese on Saturday handed Inter their 17th scudetto and fourth in a row.
Inter, who still have three games left to play, were supposed to celebrate at their training ground but made a late decision to take a bus to Piazza Duomo, the city's main square, where thousands of flag-waving fans were waiting.
City officials then had to undertake a major clean-up operation with the ninth stage of cycling's Giro d'Italia taking place in Milan later on Sunday, before Inter party again in their home match with Siena (1830 GMT).
Coach Jose Mourinho, in his first season in charge, was humbled by the success.
"It is thanks to everyone. The staff, coaches ... even the cleaning lady who works in the shadows," the Portuguese, who also won league titles with Porto and Chelsea, told reporters.
"In the history of Inter many others have done better than me and I understand soccer, I know that without results there is not this passion so I have to continue on this path to stay in the hearts of these people."