The French invaded the Netherlands, with Napoleon defeating the Prussians at Ligny, and Marshal Ney engaging indecisively with Wellington at the Battle of Quatre Bras. The Prussians retreated 18 miles north to Wavre whilst Wellington's Anglo-Allied army withdrew 15 miles north to a site he had noted the previous year as favourable for a battle: the north ridge of a shallow valley on the Brussels road, just south of the small town of Waterloo. On 17 June there was torrential rain, which severely hampered movement and had a considerable effect the next day, 18 June, when the Battle of Waterloo was fought. This was the first time Wellington had encountered Napoleon; he commanded an Anglo-Dutch-German army that consisted of approximately 73,000 troops, 26,000 of whom were British. Approximately 30 percent of that 26,000 were Irish.