The Phoenicians and their successors, the Carthaginians, were particularly adept sailors and learned to voyage further and further away from the coast in order to reach destinations faster. One tool that helped them was the sounding weight. This tool was bell shaped, made from stone or lead, with tallow inside attached to a very long rope. When out to sea, sailors could lower the sounding weight in order to determine how deep the waters were, and therefore estimate how far they were from land. Also, the tallow picked up sediments from the bottom which expert sailors could examine to determine exactly where they were. The Carthaginian Hanno the Navigator is known to have sailed through the Strait of Gibraltar c. 500 BC and explored the Atlantic coast of Africa. There is general consensus that the expedition reached at least as far as Senegal. There is a lack of agreement whether the furthest limit of Hanno's explorations was Mount Cameroon or Guinea's 890-metre (2910-foot) Mount Kakulima. Nonetheless, Hanno's maritime travels limit may have been further north, as there are well documented difficulties with the return travel from the regions south of cape Chaunar, which, up to the early 15th century, "had hitherto been the non plus ultra or impassable limit of European navigation"