Arteries in general are thicker than veins because of the nature of their purpose in the circulatory system. Arteries are the first tissue near the heart that will be used in pumping the blood. In this connection, arteries should be flexible in sudden change of pressure in order to control the nature of blood flow. That is why it is full of muscles in order to add rigidity to the artery. Veins on the other hand are the ones that bring the blood back to the heart. There is no need of much pressure in doing that as compared to the function of the arteries.