Complex sentence: At around 6:00 pm the Polish king ordered the cavalry attack in four groups, three Polish and one from the Holy Roman Empire--18,000 horsemen charged down the hills, the largest cavalry charge in history.
Split into simpler sentences: At around 6:00 pm the Polish king ordered the cavalry attack in four groups, three Polish and one from the Holy Roman Empire. Eighteen thousand horsemen charged down the hills, the largest cavalry charge in history.