In English law, poundage was an ad valorem (in proportion to value) customs duty imposed on imports and exports at the rate of 1 shilling for every pound (of weight) of goods imported or exported. Poundage was implemented in order to keep a strong naval force that would protect the Kingdom of England. The custom duty would allow the Monarch of the Kingdom to collect money that would then be spent to develop and maintain the naval force that protects the Kingdom. Poundage was closely associated with tonnage, or tunnage, which was a duty on every tun of wine imported.