At last Cromwell was himself again. In the first days of June Charles's new army lay at Stirling. The seizure and imprisonment of his English partisans had deprived him of all hope of raising a diversion in the south, and Leslie was compelled to fall back on the defensive tactics by which he had guarded Edinburgh the year before. During the first fortnight of July Cromwell laboured in vain to bring on an engagement. Leslie, strongly posted amongst the hills to the south of Stirling, was not to be induced to repeat the error he had committed at Dunbar, and this time provisions and water could be obtained without difficulty. If Cromwell did not intend to waste his army away, he must transfer it to the enemy's rear, with a certain result of leaving the road open for their advance into England. Six months before, whilst the chiefs of English royalism were still at large, it would have been a most hazardous plan. Now that they were under arrest, it might be attempted with impunity. Lambert was sent across to North Queensferry, and on July 20 he defeated, at Inverkeithing, a Scottish force sent out from Stirling against him. Before long Cromwell followed his lieutenant, and on August 2 Perth fell into his hands. The communications of the Scottish army at Stirling were thus cut, and there was nothing before it but to march southwards on the uncertain prospect of being still able to find allies in England. That Cromwell had been able to accomplish this feat was owing partly to his command of the sea, which had enabled him with safety to send Lambert across the Forth, partly to his knowledge that the materials of the Scottish army were far inferior to those of his own. Had Leslie been at the head of a force capable of meeting the invaders in the field, Cromwell at Perth might indeed have found himself in an awkward position, as, in case of defeat, he might easily have been driven back to perish in the Highlands. On the other hand, it must be acknowledged that the English General had been learning from his opponent. It was now--unless the campaign of Preston be excepted, when his march upon Hamilton's flank had been decided by the necessity of picking up his artillery in Yorkshire--that Cromwell, for the first time in his life, developed strategical power, that is to say, the power of combining movements, the result of which would place the enemy in a false position. Already, before he followed Lambert, he had summoned Harrison to Linlithgow, and had ordered him to keep the Scots in check as they marched through England.