Up until the Renaissance, technological navigation stayed rather primitive, but this didn't hold back some civilisations from becoming sea powers. The Byzantine navy and the Vikings are a couple of examples. The design of ships started to change towards the end of the 14th century with ships such as the carrack using towers on the bow and stern. This hampered the ships stability and by the 15th century, the caravel had been designed by the Portuguese. It was based on the Arabic qarib and was able to sail closer to the wind and became more widely used. Gradually, the towers were replaced by the foreastle and sterncastle. This also allowed for another innovation, the freeing port and associated artillery. In the 16th century, these structures became widespread on galleons. Galleons included multiple decks and a versatility that allowed them to be used either as trading or war ships. Ships in Asia were developing much the same way as in Europe. During the 15th century, China's Ming Dynasty gathered together one of the largest and most powerful naval fleets. Whereas in Japan, one of the world's first iron ships was also developed. During this time there was an increase in foreign commerce with more and more ships sailing to and coming from Arabia, India, Venetia, Persia, Egypt, Portugal and even China. Cloth and spices were traded for gold, wax and ivory.