In order to keep the trade strictly under control and to properly protect it, intercourse with the colonies was held only once a year. Two squadrons, consisting of merchant ships and convoys under command of an admiral and vice-admiral, made the trip each year. The fleet for New Spain (Mexico) sailed in the spring, and that for the mainland in the early fall. The first touched at some of the islands and then went to Vera Cruz; the latter touched first at Cartagena and passed on thence to Porto Bello, where the fair was held about the middle of March. This fair was the great event of the year, and lasted forty days from the time of the arrival of the fleet. From this point goods were distributed by way of Panama to Peru, Chile, and even across the continent to Buenos Aires. The gold bullion was sent in turn to this point by the viceroy of Peru. It came in fifteen days from Potosi to Arica, thence by sea in eight days to Callao, and in twenty days from Callao to Panama. The viceroy of Peru was to take care to have the plate at Panama by the middle of March. At Porto Bello it was taken aboard the galleons. About the middle of June the galleons met the fleet from New Spain at Havana, and from that point the two fleets with their convoys proceeded in greater safety to Spain. Thus for two centuries all intercourse between Spain and her colonies at one end of the line was limited at first to Seville, and then to Cadiz; and at the other to Vera Cruz and Porto Bello.[11] At a later period this arrangement was modified to some extent, and Buenos Aires was made a port of entry. The reason for not permitting trade with Buenos Aires during the earlier period was the fear that the British and Dutch would smuggle through that port. While the relations of the colonies with Spain were kept under the strictest control, intercourse with foreign nations, although absolutely prohibited under the severest penalties, could not be entirely prevented. In speaking of Spain's restrictive policy, a British naval officer, who was on the South American station during the revolution, says: