Then the duke gave the order for the whole cavalry to advance.

Headed by the English dragoons, they came down in good order through the concentrated fire of the enemy's batteries to the edge of the stream; but the difficulties here were immense.

The stream was divided into several branches, with swampy meadows between them, and only by throwing down fascines could a footing be obtained for the horses.
"I don't call this fighting, Master Rupert," Hugh said, as they floundered and struggled through the deep marshes, while the enemy's shell burst in and around the ranks; "it's more like swimming.

Here come the French cavalry, and we've not even formed up." Had the French charge been pressed home, the dragoons must have been crushed; but Churchill's infantry on their right opened such a heavy fire that the French cavalry at that end of the line paused.
On their left, however, near Blenheim, the dragoons, suffering terribly from the artillery and musketry fire from that village, were driven back by the French cavalry to the very edge of the swamp.
Marlborough, however, anxiously watching the struggle, continued to send fresh bodies of horse across to their assistance, until the Dutch and Hanoverian squadrons were all across, and the allied cavalry formed in two long lines.
While this had been going on, a serious fight had been raging in front of Oberglau; and here, as at Blenheim, the allies suffered disaster.

Here the Hanoverians, led by the Prince of Holstein, had attacked.