The progress of the siege had been marked by surprising energy, but it was prolonged by the resolute defence of the garrison; and when all things were ready for a general assault, a French army of overwhelming numbers, commanded by Marshal Schomberg, advanced to its relief. The Prince of Orange immediately raised the siege and retired; and the three English regiments, having sustained a severe loss, and having nearly half the number of the surviving officers and men wounded, were sent into quarters of refreshment in Holland. At the same time a misunderstanding occurred between Colonel (afterwards Sir John) Fenwick and the Prince, and the Colonel resigned his commission; when his Highness gave the Colonelcy of the regiment to the Lieutenant-Colonel, Henry Wisely. [Sidenote: 1677] The French, while amusing the Allies with negotiations for a peace, commenced the campaign of 1677, with great vigour, and with such an immense army, that the feeble preparations of the Dutch, and the apathy of the Spaniards, left the Prince of Orange without an army capable of resisting the enemy. He, however, resolved to attempt the relief of St. Omers, which was besieged by the French; the English Brigade was ordered to West Flanders, to take part in the enterprise, and it was encamped a short time on the plains of the Yperlee. In the early part of April, the Prince advanced with his little army, and on the 11th of that month he fought the battle of _Mont-Cassel_ under great disadvantages in numbers, and in the nature of the ground. The English Brigade behaved with its usual gallantry; but the army was defeated, and the Prince retreated with the loss of his baggage and artillery. The Brigade was afterwards employed in manœuvring and in defensive operations until the autumn, when it went into quarters. The Prince of Orange proceeded to England, and was married to the Princess Mary on the 14th of November, 1677. [Sidenote: 1678] Before the following spring, Major-General the Earl of Ossory arrived from England to command the six British regiments in the Dutch service, and ten thousand English troops, commanded by the Duke of Monmouth, were ordered to proceed to Flanders to take part in the war. The Earl of Ossory's brigade was early in the field: it was employed a short time on detached services in the Netherlands, and was afterwards encamped near the ground where the battle of Waterloo was fought in June, 1815. In the mean time the French besieged _Mons_, the capital of the province of Hainault, and their covering army occupied a strong position, with its right at the Abbey of _St. Denis_, and its left at Mamoy St. Pierre. The Prince of Orange assembled his army, and after advancing several stages, he encamped near the little river Senne, about seven miles from Mons; and on the morning of the 14th of August, 1678, his Highness put the troops in motion to attack the enemy.