[Footnote 15: Principles of International Law, p. 526. The older writers differed from this view. Grotius maintained the right of passage, even by force; Vattel practically agreed with Grotius that it might be taken by force, but contended that it should be asked and force used only under extreme necessity, or when the refusal was unjust; Wheaton denied that the right of passage was a "perfect right" and consequently could not be enforced against the will of the neutral; Hall, International Law (1880), §219, points out that more recent writers take an opposite view, namely, that a grant of passage is incapable of impartial distribution. See also Wheaton, International Law, §427; Vattel, Droit des gens, III, §110; Calvo, Droit international, 3d Ed., III, §§2344-2347.] Mr. Baty, who has made a careful study of the precedents upon the subject, states that while "writers vary in their treatment of the question" of the passage of troops over neutral territory, "the modern authorities are all one way."[16] He points out that the jurists of the first half of the nineteenth century, with the possible exception of Klüber, were "unanimous in following" Grotius and Vattel, and allowing neutrals to permit belligerents passage as long as they did it impartially. But since the middle of the century a total and violent change in the opinion of authors has operated. Every modern author holds that passage is now a benefit which must be refused absolutely, and not offered impartially.[17] [Footnote 16: International Law in South Africa, p. 71.] [Footnote 17: Ibid., p. 73.] [Footnote 18: Times Military History of the War in South Africa, Vol. IV, p. 369] In February the Transvaal Government had attempted to bring troops into Rhodesia by way of Portuguese territory. Portugal had promptly sent out forces to prevent such an evasion of Portuguese neutrality and had guarded the railway bridges along the line to Rhodesia. And in March Great Britain had met with a refusal to allow a large quantity of foodstuffs, mules, and wagons to be landed at Beira for the purpose of transportation to Rhodesia. Nevertheless, on April 9, General Sir Frederick Carrington landed at Cape Town under orders to proceed immediately to Beira.[18] He was to use transports put at his disposal by his government for the purpose of collecting a full equipment for his command of five thousand men to be mobilized at Beira, and from that port was to enter Rhodesia. This province was then to be made the base for an expedition against Pretoria in concert with the English forces advancing from the south.