For instance, on the 25th of May Marlborough's forces were approaching Coblentz. To find out what they were going to do next, the French would have to know whether they were beginning to turn up the valley of the Moselle, which begins at Coblentz, or to cross that river and be going on further south. A messenger might have been certain that the latter was their intention by midday of the 26th, but Tallard, right away on the Upper Rhine, would hardly have known this before the morning of the 29th, and by the morning of the 29th Marlborough was already opposite Mayence. It is this gap of from one to three days in the passage of information which is so difficult for a modern man to seize, and which yet made possible all Marlborough's manoeuvres to confuse the French. Villeroy was bound to watch until, at least, the 29th of May for the chance of a campaign upon the Moselle. Meanwhile, Tallard was not only far off in the valley of the Upper Rhine, but occupied in a remarkable operation which, had he not subsequently suffered defeat at Blenheim, would have left him a high reputation as a general. This operation was the reinforcement of the army under the Elector of Bavaria and Marcin by a dash right through the enemy's country in the Black Forest. Early in May the Elector of Bavaria had urgently demanded reinforcements of the French king. The mountains between the Bavarian army and the French were held by the enemy, but the Elector hurried westward along the Danube, while Tallard, with exact synchrony and despatch, hurried eastward; each held out a hand to the other, as it were, for a rapid touch; the business of Tallard was to hand over the new troops and provisions at one exact moment, the business of the Elector was to catch the junction exactly. If it succeeded it was to be followed by a sharp retreat of either party, the one back upon the Danube eastward for his life, the other back westward upon the Rhine. Tallard had crossed the Rhine on the 13th of May with a huge convoy of provisionment and over 7000 newly recruited troops. Within a week the thing was done. He had handed over in the nick of time the whole mass of men and things to the Elector.[2] He had done this in the midst of the Black Forest and in the heart of the enemy's country, and he immediately began his retirement upon the Rhine. Tallard was thus particularly delayed in receiving daily information of Marlborough's march. Let us take a typical date.