Marlborough's march started on 19 May from Bedburg, 32 kilometres (20 mi) northwest of Cologne.
The army (assembled by the Duke's brother, General Charles Churchill) consisted of 66 squadrons, 31 battalions and 38 guns and mortars totalling 21,000 men (16,000 of whom were English troops).
This force was to be augmented en route such that by the time Marlborough reached the Danube, it would number 40,000 (47 battalions, 88 squadrons).
Whilst Marlborough led his army, General Overkirk would maintain a defensive position in the Dutch Republic in case Villeroi mounted an attack.
The Duke had assured the Dutch that if the French were to launch an offensive he would return in good time, but Marlborough calculated that as he marched south, the French commander would be drawn after him.
In this assumption Marlborough proved correct: Villeroi shadowed the Duke with 30,000 men in 60 squadrons and 42 battalions.

The military dangers in such an enterprise were numerous: Marlborough's lines of communication along the Rhine would be hopelessly exposed to French interference, for Louis' generals controlled the left bank of the river and its central reaches.
Such a long march would almost certainly involve a high wastage of men and horses through exhaustion and disease.
However, Marlborough was convinced of the urgency – "I am very sensible that I take a great deal upon me", he had earlier written to Godolphin, "but should I act otherwise, the Empire would be undone ..."
Whilst Allied preparations had progressed, the French were striving to maintain and re-supply Marshal Marsin.
Marsin had been operating with the Elector of Bavaria against the Imperial commander, Prince Louis of Baden, and was somewhat isolated from France: his only lines of communication lay through the rocky passes of the Black Forest.
However, on 14 May, with considerable skill Marshal Tallard managed to bring 10,000 reinforcements and vast supplies and munitions through the difficult terrain, whilst outmanoeuvring Baron Thüngen, the Imperial general who sought to block his path.
Tallard then returned with his own force to the Rhine, once again side-stepping Thüngen's efforts to intercept him.
The whole operation was an outstanding military achievement.

On 26 May, Marlborough reached Coblenz, where the Moselle meets the Rhine.
If he intended an attack along the Moselle the Duke must now turn west, but, instead, the following day the army crossed to the right bank of the Rhine, (pausing to add 5,000 waiting Hanoverians and Prussians). "
There will be no campaign on the Moselle", wrote Villeroi who had taken up a defensive position on the river, "the English have all gone up into Germany."
A second possible objective now occurred to the French – an Allied incursion into Alsace and an attack on the city of Strasbourg.
Marlborough skilfully encouraged this apprehension by constructing bridges across the Rhine at Philippsburg, a ruse that not only encouraged Villeroi to come to Tallard's aid in the defence of Alsace, but one that ensured the French plan to march on Vienna remained paralysed by uncertainty.

With Villeroi shadowing Marlborough's every move, Marlborough's gamble that the French would not move against the weakened Dutch position in the Netherlands paid off.
In any case, Marlborough had promised to return to the Netherlands if a French attack developed there, transferring his troops down the Rhine on barges at a rate of 130 kilometres (80 miles) a day.
Encouraged by this promise (whatever it was worth) the States General agreed to release the Danish contingent of seven battalions and 22 squadrons as a reinforcement.
Marlborough reached Ladenburg, in the plain of the Neckar and the Rhine, and there halted for three days to rest his cavalry and allow the guns and infantry to close up.
On 6 June he arrived at Wiesloch, south of Heidelberg.
The following day, the Allied army swung away from the Rhine towards the hills of the Swabian Jura and the Danube beyond.
At last Marlborough's destination was established without doubt.
Marlborough's march started on 19 May from Bedburg, 32 kilometres (20 mi) northwest of Cologne. The army (assembled by the Duke's brother, General Charles Churchill) consisted of 66 squadrons, 31 battalions and 38 guns and mortars totalling 21,000 men (16,000 of whom were English troops). This force was to be augmented en route such that by the time Marlborough reached the Danube, it would number 40,000 (47 battalions, 88 squadrons). Whilst Marlborough led his army, General Overkirk would maintain a defensive position in the Dutch Republic in case Villeroi mounted an attack. The Duke had assured the Dutch that if the French were to launch an offensive he would return in good time, but Marlborough calculated that as he marched south, the French commander would be drawn after him. In this assumption Marlborough proved correct: Villeroi shadowed the Duke with 30,000 men in 60 squadrons and 42 battalions.
The military dangers in such an enterprise were numerous: Marlborough's lines of communication along the Rhine would be hopelessly exposed to French interference, for Louis' generals controlled the left bank of the river and its central reaches. Such a long march would almost certainly involve a high wastage of men and horses through exhaustion and disease. However, Marlborough was convinced of the urgency – "I am very sensible that I take a great deal upon me", he had earlier written to Godolphin, "but should I act otherwise, the Empire would be undone ..."
Whilst Allied preparations had progressed, the French were striving to maintain and re-supply Marshal Marsin. Marsin had been operating with the Elector of Bavaria against the Imperial commander, Prince Louis of Baden, and was somewhat isolated from France: his only lines of communication lay through the rocky passes of the Black Forest. However, on 14 May, with considerable skill Marshal Tallard managed to bring 10,000 reinforcements and vast supplies and munitions through the difficult terrain, whilst outmanoeuvring Baron Thüngen, the Imperial general who sought to block his path. Tallard then returned with his own force to the Rhine, once again side-stepping Thüngen's efforts to intercept him. The whole operation was an outstanding military achievement.
On 26 May, Marlborough reached Coblenz, where the Moselle meets the Rhine. If he intended an attack along the Moselle the Duke must now turn west, but, instead, the following day the army crossed to the right bank of the Rhine, (pausing to add 5,000 waiting Hanoverians and Prussians). "There will be no campaign on the Moselle", wrote Villeroi who had taken up a defensive position on the river, "the English have all gone up into Germany." A second possible objective now occurred to the French – an Allied incursion into Alsace and an attack on the city of Strasbourg. Marlborough skilfully encouraged this apprehension by constructing bridges across the Rhine at Philippsburg, a ruse that not only encouraged Villeroi to come to Tallard's aid in the defence of Alsace, but one that ensured the French plan to march on Vienna remained paralysed by uncertainty.
With Villeroi shadowing Marlborough's every move, Marlborough's gamble that the French would not move against the weakened Dutch position in the Netherlands paid off. In any case, Marlborough had promised to return to the Netherlands if a French attack developed there, transferring his troops down the Rhine on barges at a rate of 130 kilometres (80 miles) a day. Encouraged by this promise (whatever it was worth) the States General agreed to release the Danish contingent of seven battalions and 22 squadrons as a reinforcement. Marlborough reached Ladenburg, in the plain of the Neckar and the Rhine, and there halted for three days to rest his cavalry and allow the guns and infantry to close up. On 6 June he arrived at Wiesloch, south of Heidelberg. The following day, the Allied army swung away from the Rhine towards the hills of the Swabian Jura and the Danube beyond. At last Marlborough's destination was established without doubt.
Battle of Blenheim