Although according to the Roman law the sea was common and free to all, in the middle ages many seas had become more or less effectively appropriated, and Civilian writers began to assign to maritime states, as a principle of law, a certain jurisdiction in the waters adjacent to their coasts. The distance to which such jurisdiction was allowed by those writers was variously stated. Very commonly it extended to sixty or one hundred miles from the land, and thus included all the bordering sea within which navigation was practically confined. Sometimes the principle governing the ownership of rivers was transferred in theory to the sea, the possession of the opposite shores by the same state being held to entitle that state to the sovereignty over the intervening water; or, if it possessed only one shore, to the same right as far as the mid-line. In most cases, however, the appropriation of the sea was effected by force and legalised afterwards, if legalised at all, and the disputes on the subject between different nations not infrequently led to sanguinary wars. The most notable instances are to be found among the early Italian Republics. Long before the end of the thirteenth century Venice, eminent for her commerce, wealth, and maritime power, assumed the sovereignty over the whole of the Adriatic, though she was not in possession of both the shores, and after repeated appeals to the sword she was able to enforce the right to levy tribute on the ships of other peoples which navigated the Gulf, or to prohibit their passage altogether. The neighbouring cities and commonwealths were soon compelled to agree to her claim, which was eventually recognised by the other Powers of Europe and by the Pope. The right of Venice to the dominion of the Adriatic, arising in this way by force, became firmly established by custom and treaty; and even after she had fallen from her greatness and was hardly able to sustain her claim by the sword, it was still for a time admitted by other nations, who looked upon the Republic as forming a useful barrier to the farther extension of the Turk in Europe and as a scourge to the Saracen pirates.[1] On the other side of the Italian peninsula, the Republic of Genoa advanced a similar claim to the dominion of the Ligurian Sea, and some of the other Mediterranean states followed the example in the waters with which they were most immediately concerned.