In just a couple of weeks, Celtic will start their European campaign against FC Stjarnan of Iceland, a far cry from some of the great names the Old Firm have butted heads with in European competition over the years. A potential fairy tale run is never too far away from Scotland's two biggest clubs though, and Celtic are no doubt due another clash with one of the heavyweights again this season. Rangers are not without glory on the continent either, their longest absence from European football in decades helps those memories occupy a special place in the hearts of Gers fans everywhere. And somewhat ironically, the two clubs have excelled as underdogs, despite being the undisputed top dogs in their domestic competitions. As long as the league continues to be classed as being on a secondary level, that looks likely to continue. From Lisbon to Seville, Barcelona to Manchester, glory to pain, here are 10 of the greatest moments that fans of the Old Firm have been treated to over the years.