In the 18th century, the sand bars of the Guadalquivir forced the Spanish government to transfer its American trade from Seville to Cádiz, which now commanded better access to the Atlantic. Although the empire itself was declining, Cádiz now experienced another golden age from its new importance. It became one of Spain's greatest and most cosmopolitan cities and home to trading communities from many countries, the richest of which were the Irishmen. Many of today's historic buildings in the Old City date from this era.