True, but Martel was Charlemagne's grandfather. I think Cato was referring to Charlemagne's expedition to Spain, when some say he so weakened the Spanish Islamic state that it could not make a planned invasion of the Frankish state. That was the expedition on which Charlemagne left his captains Roland and Oliver in command of a rearguard force in the Pyrenees, which was famously wiped out, before Charlemagne could return, summoned by the horn of Roland!