Killed at the Battle of Brissarthe while defending Francia against a joint Breton-Viking raiding party led by Salomon, King of Brittany and the Viking chieftain Hastein. During the battle the Viking commander was entrapped in a nearby church. Robert removed his armour to start to besiege the church; now the Vikings launched a surprise attack and he died in the melee. His heroic successes against the Vikings led to his characterisation as "a second Maccabaeus" in the Annales Fuldenses.

http://en.wikipedia.org/wiki/Robert_the_Strong