It was while the northerly states of Greece were thus successively falling off from the common cause, that the deputies assembled at the Isthmus took among themselves the solemn engagement, in the 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 favor of those states which had been driven to yield by irresistible necessity.[128] 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. [128] Herodot. vii, 132; Diodor. xi, 3. 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, etc., 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. On the northern portion of Eubœa, immediately facing Magnesia and Achæa Phthiôtis, was situated the line of coast called Artemisium: a name derived from the temple of Artemis, which was its most conspicuous feature, belonging to the town of Histiæa. It was arranged that the Grecian fleet should be mustered there, in order to coöperate with the land-force, and to oppose the progress of the Persians on both elements at once. To fight in a narrow space[129] was supposed favorable to the Greeks on sea not less than on land, inasmuch as their ships were both fewer in number and heavier in sailing than those in the Persian service. From the position of Artemisium, it was calculated that they might be able to prevent the Persian fleet from advancing into the narrow strait which severs Eubœa, to the north and west, from the mainland, and which, between Chalkis and Bœotia, becomes not too wide for a bridge. It was at this latter point that the Greek seamen would have preferred to place their defence: but the occupation of the northern part of the Eubœan strait was indispensable to prevent the Persian fleet from landing troops in the rear of the defenders of Thermopylæ. [129] Herodot. viii, 15-60. Compare Isokratês, Panegyric, Or. iv, p. 59. I shall have occasion presently to remark the revolution which took place in Athenian feeling on this point between the Persian and Peloponnesian wars.