It is important to note--what many of his followers too often forgot--that Grotius restricts the application of his general argument for _mare liberum_ to the open sea. He does not, he says, deal with an inland sea (_mare interiore_) which, surrounded on all sides by land, did not exceed the breadth of a river; the question concerned the ocean, which the ancients called immense, infinite, the parent of things, co-terminous with the air. The controversy, he continues, was not about a bay or a strait in this ocean, _nor concerning so much of it as might be seen from the shore_: the Portuguese claim for themselves whatever lies between the two worlds.[622] Again, referring to the Italian publicists, he says their opinion cannot be applied to the matter in question, for they speak of the Mediterranean, he of the ocean; they of bays or gulfs, he of the vast sea, which differ very much in respect of occupation.[623] The opinions and reasonings of Grotius in _Mare Liberum_ as to the free use of the sea were repeated more concisely and with some modification in his greatest work, _The Rights of War and Peace_, which was published in 1625.[624] No one, he affirmed, can have property in the sea, either as to the whole or its principal parts; and as some people admit this in respect to private persons but not in regard to countries or states, he proceeds to prove its truth by both a “moral reason and a natural reason.” The moral reason is the vast extent and inexhaustibility of the sea, whether for navigation or fishing; the natural reason is that it cannot be occupied or possessed because of its fluidity, since liquids having no bounds of their own cannot be possessed unless enclosed by something else, as a river by its banks; but the sea is not contained in the earth, as it is equal to it or even greater.[625] Grotius, however, admits that his argument that rivers and lakes may be appropriated because their banks could be appropriated, may be logically applied also to certain parts of the sea. From the example of rivers he says, “It appears that the sea may be occupied by him who is in possession of the lands on both sides, although it be open either above, as a bay or gulf, or both above and below, as a strait, provided that it be not so great a part of the sea that when compared with the lands on each side it cannot be supposed to be some part of them”; and what is lawful to one king or people may be also lawful to two or three, if they have a mind to take possession of the sea thus enclosed within their land.[626] He also admits by another train of reasoning--concerning property in the marine vivaria of the Romans--that if it is not repugnant to the law of nature for a private person to appropriate a small enclosed part of the sea, one or more nations possessing the shores might in like manner appropriate a part of the sea, if it be small compared with the land; and that might happen although the sea was not enclosed on all sides.