[Footnote 242: Thus Nordenskjöld sums up after an exhaustive review of all the chief early portolans: "Not only are the coast-legends the same, even the ... names in red ink of places considered of special importance to navigators were not essentially different in the three centuries from Vesconte to Voltius. Moreover: (1) The Mediterranean and Black Sea have exactly the same shape on all these maps; (2) a distance-scale, with the same unit of length, such as otherwise is used only on the Spanish and French Mediterranean coasts, occurs on all these maps, independently of the land of their origin; (3) the distances across the Mediterranean and Black Sea, measured with this scale, agree perfectly on the islands and capes remain almost unaltered on portolanos from the fourteenth to the sixteenth century. So that it may be thought proved that all these portolanos are only amended codices of the same original" (_Periplus_, 45 A).] [Footnote 243: _E.g._, Nordenskjöld, in his last work (_Periplus_, 46, 47).] [Footnote 244: Nordenskjöld conjectures probably between 1266 and 1300.] These plans of practical seamen are a striking contrast, in their often modern accuracy, to the results of the literary or theological geography portrayed in such works as those of the "Beatus School," or of Robert of Haldingham.[245] Map surveys of this kind were apparently unknown to the ancient world. The old _Peripli_ were sailing directions, not drawn but written; and the only Arabic portolan known to exist was copied from an Italian example. Long after the Italian leadership in exploration and commerce had begun to pass away, Italian science kept control of cartographical work; thus, among the early portolani, not only the majority--413 out of 498--but the most valuable, were executed by the countrymen of Carignano and Vesconte. [Footnote 245: Cf. (1) the Beatus maps of "St. Sever," "Ashburnham," "Turin," "London," of 1109, "Valladolid," "Madrid," etc., of the tenth, eleventh, and twelfth centuries; (2) the Hereford _Mappemonde_ of the late thirteenth century, with which may be compared the Ebstorf world-map of c. 1300; see Konrad Miller, _Die ältesten Weltkarten_, Heft v, 1896.]