Complex sentence: Hasdrubal was camped approximately a half-mile to the North, however, since Claudius Nero had conveniently arrived at night, his presence was not detected until the next day, when the Romans drew themselves up for battle.
Split into simpler sentences: Hasdrubal was camped approximately a half-mile to the north. However, since Claudius Nero had conveniently arrived at night, his presence was not detected until the next day, when the Romans drew themselves up for battle.