When Columbus anchored in the Tagus River, March 5, 1493, he precipitated on Europe one of the most difficult questions with which the mind of man has ever grappled. It was this: By what title should the New World be held ? The Catholic sovereigns Ferdinand and Isabella determined to hold what their Admiral had discovered. But the Spanish lawyers found great difficulty in proving their title under the Roman law, which alone would be accepted as conclusive by the other powers, because it did not recognize the right of discovery. The Roman law recognized the acquisition of property through the operation of either the jus gentium or the jus civile? Under the jus gentium, which alone was applicable in this case, property could be acquired: ist, by occupation, occupatio; 2d, by natural increase, as land formed by seas or rivers, accessio; 3d, by transfer, traditio. The only doctrine suitable to the purposes of Spain was that of “occupation,” which some eminent Roman lawyers incorporated not in the jus gentium but in the jus natura, as affirming a natural right.