Complex sentence: He marched from Glogau to Kolberg in 13 days, 5--18 September, and on the same day he arrived there he immediately attacked the surprised Russians, who left their camp in panic and withdrew to Poland.
Split into simpler sentences: He marched from Glogau to Kolberg from 5 to 18 September and on the same day he surprised the Russians by attacking off the march. The Russians were routed, left their camp in panic and withdrew to Poland.