The UEFA Cup in 1999 was a special event for Mainz 05, highlighting the club's ambitions to establish itself in the European football landscape. In the first round, the Nullfünfer faced Celtic Glasgow, one of Scotland's most storied clubs. The matches against Celtic were not only a challenge on the pitch but also an opportunity for the fans to show their passion and support for the team.

The first leg took place on September 16, 1999, at Mainz's stadium. The atmosphere was electric as supporters cheered their team from the stands. Mainz 05 put in a solid performance, even though they faced a strong opponent. The return leg in Glasgow presented an even greater challenge, but the Nullfünfer proved that they could compete not just on a national level but also in the European arena.

The encounters with Celtic were a milestone for Mainz 05. While the club did not achieve significant success in the UEFA Cup, the experience of facing such an opponent was invaluable. These matches led to a stronger identity and greater confidence within the team and the club. Fans fondly remembered the passionate support and thrilling moments as the Nullfünfer took on one of the world's most recognized teams on the European stage.

At a time when Mainz 05 did not yet enjoy the establishment they have today, this appearance on the European stage was an important sign of the club's development. It demonstrated that Mainz 05 was ready to face the challenges of international football. The memories of the UEFA Cup in 1999 remain a part of the club's DNA, inspiring the current generation of players and fans to continue striving for greater heights.