With regards to the economy, collection of taxes was more efficient under the intendancy system. In 1778, Charles III established the "Decree of Free Trade," which allowed the Spanish American ports to trade directly with one another and most ports in Spain. Therefore, "commerce would no longer be restricted to four colonial ports (Veracruz, Cartagena, Lima/Callao, and Panama)." Tax reductions were given to the silver mining industry as part of the Crown's attempts to stimulate silver production, which had plummeted throughout Spanish America at the beginning of the 1700s. Spain relied heavily on the silver industry for tax revenue, particularly on the mines at Potosí in the Andes. In 1736, the Crown reduced the tax on silver from one-fifth to one-tenth in order to encourage silver production to be reported. Over the course of the 18th century, the market for silver led the port city of Buenos Aires to prominence, and between 1776 and 1783, 80% of the exports leaving the port at Buenos Aires were shipments of silver.