A date that saw the beginning of a journey that would change the course of history for Barcelona, October 16 will forever be seen as a watershed moment at the Camp Nou club.
It was on that date in 2004 when Lionel Messi made his official debut for the club, appearing as a substitute in La Liga and initiating a career that has since seen him play almost 600 games for the team and score well over 500 goals.
He has broken records, lifted trophies, hauled the team to success and become the world's greatest player in the eyes of many—both now and all time—and Messi's legacy will never be forgotten.
On the anniversary of his breakthrough, we look back at his debuts in different competitions in turn and assess the impact of the then-teenager in each one.
Unofficial and International Debuts
It's worth remembering Messi's journey to the Barcelona first team started many years previously; his initial trial with the club came in 2000, and it wasn't until 2003/04 that the 16-year-old Messi had progressed to youth A-team level.
A call-up to train with the seniors during an international break saw him feature in a friendly as a late substitute in November 2003 against Jose Mourinho's FC Porto.
As ESPN FC's Dermot Corrigan reported, Messi later told a Barcelona TV programme the moment was a "dream come true" and that the date, November 16, was of immense importance to him. It would be almost another year before he made his competitive debut, though.
For Argentina, his debut came in 2005 against Hungary. Had we been ranking international debuts too, this one would have featured dead last.
Messi came on as a second-half sub against Hungary, and was sent off two minutes later for a perceived elbow on an opponent.
6. Copa del Rey
It is sometimes suggested that great dynasties have humble beginnings; that couldn't be more apt in the case of Messi and his first start for Barcelona.
That memorable day—to him, if not the club in this case—came on October 27, 2004, just 11 days after his official debut as a substitute.
Messi lined up alongside Henrik Larsson and Ludovic Giuly in the attack, with the likes of Xavi, Andres Iniesta, Rafael Marquez and Carles Puyol all in the lineup too, but it was a humbling occasion as the giants suffered an embarrassing 1-0 loss at the hands of UDA Gramenet.
Then a third-tier side, Gramenet won thanks to a goal from an ex-Barca youth player Oscar Olles, with El Pais' report noting Barca's "big defect was a lack of [potent] attack."
That was not a great sign of what was to come with Messi in the front line, in fairness.
5. UEFA Champions League
Messi debuted in three competitions in his first five matches for Barcelona's senior team, with a first European appearance coming in December 2004.
It was a group-stage dead rubber, with Messi only having been an unused sub at that point in the Champions League against AC Milan twice. His first taste on a continental pitch came at Shakhtar Donetsk with Barca already guaranteed a top-two finish in the group.
Messi played the full 90 minutes on this occasion but once more suffered defeat. A much-changed Barca side—though still with Puyol, Iniesta, Xavi and Victor Valdes—lost 2-0, and Messi failed to have much of an impact.
This was to be his only experience of European football that season, as he was left out of the squads for the round-of-16 legs wherein Barca were knocked out by Chelsea.
4. UEFA Super Cup
Fast forward a year and a half, and Barcelona won the Champions League, though Messi missed the run-in and the final through injury. It meant they began the 2006/07 campaign with a UEFA Super Cup showdown against Sevilla in late August—though once more, a Messi competition debut was ruined by defeat.
Their Spanish rivals, who won the previous season's UEFA Cup with a 4-0 over Middlesbrough in the final, ran out 3-0 winners against Barca in Monaco.
Messi was a regular starter by this point, one-third of the famous front line that also included Ronaldinho and Samuel Eto'o, but they were outshone by Frederic Kanoute and Co.
The man of the match on the night was Dani Alves, still a Sevilla player at this point but not for long. He left for Barca just one year later to form a formidable partnership with Messi down the right flank—but he completely outshone the Argentinian on this occasion, as his team did to Barca overall.
Messi didn't even get a mention in the UEFA match report, failing to make an impact.
He has since gone on to win and score in the event, but this Super Cup experience wasn't one to remember.
3. La Liga
So to Messi's official debut, 13 years ago on Monday.
He has gone on to play close to 400 times in the Spanish top flight since, but Messi finally became a Barcelona senior, wearing the No. 30 shirt, in mid-October 2004.
Barca won the match 1-0 thanks to Deco's early strike, and Messi came on as sub for the goalscorer for the final eight minutes of the match.
He was 17 years, three months and 22 days old, becoming the youngest competitive modern debutant for the Catalan club—though Barca's website still notes Paulino Alcantara as the official youngest, with his debut in the Campionat de Catalunya coming as a 15-year-old back in 1912.
It was just a cameo but gave fans an inkling of what was to come in the years ahead. Four youth prospects were called up to boost the depleted Barca squad that day, per the club website, but only Messi went on to have any impact whatsoever.
And that impact has seen him outscore most of the rest of the players in the history of the club combined.
2. Spanish Super Cuo
While Messi was a first-team regular in 2005/06, his end-of-season injury meant he was still on the recovery trail when the next campaign began.
He was therefore a sub against Espanyol in the Spanish Super Cup first leg, appearing for the final half-hour—and as with his Liga debut against the same opposition almost two years earlier, Barca ran out 1-0 winners.
Messi, now wearing the No. 19 shirt, replaced Giuly around the hour mark; another quirk of circumstance meant he again replaced the goalscorer on a competition debut against Espanyol in a game won by the same scoreline.
He started the second leg as Barca took the trophy 4-0 on aggregate, shortly before the aforementioned UEFA Super Cup defeat to Sevilla.
1. FIFA Club World Cup
Comfortably Messi's best competition debut came in 2009, when he finally made his bow in the FIFA Club World Cup.
Messi missed the 2006 edition because of a metatarsal fracture, and defeats to English opposition in successive campaigns meant it was 2008/09 before Barca lifted the Champions League again.
It's perhaps fitting that Messi's best club competition debut comes in the one that has the grandest, most global title; he played only part of the second half as a sub in the semi-final against Mexican outfit Atlante but took just two minutes to register a goal and send his side toward a 3-1 victory.
In the final, Messi scored the extra-time winner against Estudiantes to leave Barcelona officially the world's best club that year, a poignant moment considering his route toward the top as an individual, which started on October 16, 2004.