Complex sentence: In 837 he suppressed a revolt of Christians and Jews in Toledo and repulsed an assault by Scandinavian sea rovers in 844, and afterwards constructed a fleet and naval arsenal at Seville to repel future raids.
Split into simpler sentences: In 837 he suppressed a revolt of Christians and Jews in Toledo and repulsed an assault by Vikings in 844. Thereafter he constructed a fleet and naval arsenal at Seville to repel future raids.