The increase in size, centralization, and prosperity of the Owo and Benin kingdoms during this period is partially the result of their participation in trans-Saharan trade routes and trade with the Portuguese. Artistic production responds to refinements in metallurgic technologies and an intensified use of symbolic and ritualistic emblems of kingship. Artists of the Guinea coast are influenced aesthetically through contact with Islamic traders and the Portuguese, who often directly commission the carving of ivory objects. Additionally, the Akan (in what is now Ghana) develop an elaborate system of cast brass gold weights to measure the precious gold dust being traded to North Africa and then to Europe; the design of these gold weights is heavily influenced first by abstract Islamic visual motifs and later indigenous Akan aesthetics.