It was while the northerly states of Greece were thus successively falling oft from the common cause, that the deputies assembled at the Isthmus took among themselves the solemn engagement, in event of success, to inflict upon these recusant brethren condign punishment–to tithe them in property, and perhaps to consecrate a tenth of their persons, for the profit of the Delphian god. Exception was to be made in favour of those states which had been driven to yield by irresistible necessity. Such a vow seemed at that moment little likely to be executed: it was the manifestation of a determined feeling binding together the states which took the pledge, but it cannot have contributed much to intimidate the rest.

To display their own force, was the only effective way of keeping together doubtful allies; and the pass of Thermopylæ was now fixed upon as the most convenient point of defence, next to that of Tempê–leaving out indeed, and abandoning to the enemy, Thessalians, Perrhæbians, Magnêtes, Phthiôtid Achæans, Dolopes, Ænianes, Malians, &c, who would all have been included if the latter line had been adhered to ; but comprising the largest range consistent with safety. The position of Thermopylæ presented another advantage which was not to be found at Tempê ; the mainland was here separated from the island of Eubœa only by a narrow strait, about two English miles and a half in its smallest breadth, between Mount Knêmis and Cape Kênæum.