In the same year in which the Convention of 1818 was concluded at London between the United States and Great Britain, negotiations were being carried on at Washington between Spain and the United States, with the view of determining the effects of the Treaty of 1803, whereby Louisiana had been ceded by France to the latter power. It had been stipulated in the treaty of San Ildefonso in 1800, that Spain should retrocede "the colony or province of Louisiana, with the same extent which it now has in the hands of Spain, and which it had when France possessed it, and such as it ought to be according to the treaties subsequently made between Spain and other powers." (British and Foreign State Papers, 1817-18, p. 267-9.) The Treaty of 1803 in its turn ceded Louisiana to the United States, "in the name of the French republic, for ever and in full sovereignty, with all its rights and appurtenances, as fully and in the same manner as they have been acquired by the French republic, in virtue of the above-mentioned treaty with his Catholic Majesty." It thus became requisite to determine the limits of this new acquisition of the United States, both on the side of the Floridas, and on that of New Spain. An examination of the discussion regarding the eastern boundary towards the Floridas is unnecessary on the present occasion. The question respecting the western limit was, perhaps, the more difficult to settle, from the circumstance that Texas was claimed by Spain as a province of New Spain, whilst the United States insisted that it was a portion of Louisiana: whilst Spain contended that she had only ceded the _Spanish province_ of Louisiana, the United States maintained that she had retroceded the _French colony_. Spain thereupon proposed a line which, "beginning at the Gulf of Mexico between the River Carecut or Cascasiu, and the Armenta or Marmentoa, should go to the north, passing between Adaes and Natchitoches, until it cuts the Red River," on the ground that the Arroyo-Hondo, which is midway between Natchitoches and Adaes, had been, in fact, considered to be the boundary in 1763. The United States on the other hand, insisted on the Rio Bravo del Norte as the western frontier, on the ground that the settlement of La Salle in the Bay of St. Bernard (Matagorda) carried with it a right to the territory as far as the Rio Bravo. Beyond the Red River Spain proposed that the boundary should be determined by commissioners, after a survey of the territory, then but little known, and a reference to documents and dates, "which might furnish the necessary light to both governments upon limits which had never been fixed or determined with exactness." (State Papers, 1817-18, p. 321.) Such was the proposal made by Don Pedro Cevallos on the part of Spain, on April 9th, 1805. Messrs. Pinckney and Moore, in reply, proposed a compromise in connection with the western frontier, that a line along the River Colorado, from its mouth to its source, and from thence to the northern limits of Louisiana, should be the boundary; but the Spanish government declined to accept their proposal, and the negotiations were not resumed till the year 1817.