Obelix falls for a new arrival in his home village in Gaul, but is heartbroken when her true love arrives to visit her. However, the lovers are kidnapped by Romans; Asterix and Obelix set out to rescue them on a dangerous journey that will involve gladiators, slavers and beauracracy - and a personal encounter with the Emperor himself, Julius Caesar...
- The movie begins when Obelix falls in love with the chief's niece, Panacea. His heart is quickly broken when he hears that she is due to be married to the handsome Tragicomix. The two lovers are walking in the woods when they are captured by a group of Romans lead by a fresh new recruit looking to impress the Centurion of the Roman Camp. The Centurion is infuriated, knowing that the Gauls will attack. Panacea, Tragicomix and the new recruit are sent to the farthest outpost of the Roman empire (in the Sahara) while the Centurion and his troops prepare for the battle.
The angered Gauls trash the camp after which Asterix and Obelix are sent to find the Panacea and Tragicomix and thus end up joining the legionaries.
In the Sahara Tragicomix and Panacea manage to escape the Romans but are captured by slave traders and sold to Julius Caesar (or rather given as the humorous scene explains). After defying Caesar they are condemned as the grand finale of the Circus Maximus at the Colosseum where they will be thrown to the lions.
Asterix and Obelix trace the pair to Rome (after a brief stay in Egypt) and try to find the guy who they were sold to (the head of the Gladiator School). In a desperate effort to recruit Asterix and Obelix the owner of the Gladiator School orders their capture. They manage to capture Asterix who has lost his magic potion. That night a rainstorm flooded Asterix's cell and nearly drowned him. He is saved by Obelix who loses Dogmatix (Idéfix) who in fact has the magic potion and is bouncing around the Roman sewers which water was extremely rapid as the rainstorm causes it (the Cloaca Maxima?).
In an effort to free the lovers Asterix and Obelix join the Gladiator School. After they successfully mock up the show, Caesar unleashes the lions. Dogmatix makes a daring run across the lions' cage to the centre of the arena and gives Asterix the potion. He throws it to Tragicomix who takes care of the lions. While Obelix attempts to capture the lions he's distracted by Panacea and runs in to a pillar shattering a third of the Colosseum. With the show over and the audience evacuated Caesar grants the Gauls their freedom.
The movie ends up with the trademark victory feast that ends with the chief tripping over a rope of sausages.