A victory parade to mark Manchester United's 20th league title and Sir Alex Ferguson's retirement has drawn thousands of fans on to the streets.Many supporters gathered at the club's Old Trafford stadium as the open-top bus tour got under way.The parade travelled towards the city centre and arrived at Albert Square, where the bus was greeted by more fans.Sir Alex, who is retiring at the age of 71 after 26 years in Manchester, has won 38 trophies at Old Trafford.Speaking from the bus, the septuagenarian Scotsman thanked fans for their support over the years and for the reception he received at his final home game, United's 2-1 win against Swansea City on Sunday.He said it had been "a day I will never forget - it was wonderful"."It was something all my family enjoyed and the grandkids will never forget it."'Moment in history'The bus left the stadium via Sir Matt Busby Way - the road named after another celebrated United manager - at about 18:30 BST.Fans lined every part of the route from the stadium to the square, with police by 19:00 refusing entry to any more fans after the plaza and the surrounding streets filled to capacity.Some supporters ignited red flares, several climbed lamp posts for a view of the bus and others were seen leaning from windows and standing on rooftops.Many people travelled from far and wide to attend the parade, with some coming from as close as Stretford and others from as far away as South Africa.Famara Bojang from London said he had "come to the parade today as I wanted to be part of this moment in history", while Darren Reid from Barrow-in-Furness said he had been to "every parade since 1999, but I'm obviously here this time to say goodbye to Fergie".Ryan Giggs, who has played a part in virtually all of Sir Alex's 38 trophies, said he was happy the manager - who joined the club from Aberdeen in November 1986 - was leaving with another piece of silverware to his name.He said: "It has been tough, especially for the players who have known him for a long time. We are delighted that we were able to end on a high and won the league in his last season."During the celebrations in Albert Square, Manchester band The Courteeners played and United defender Rio Ferdinand led the crowd in singing songs about the club's players.