Arteries do not have valves. This is because the pressure from the heart is so great that valves are not needed to prevent the backflow of blood. This contrasts with veins, which do possess valves to prevent the backflow of blood.
The heart pumps blood around the body. Arteries move oxygenated blood away from the heart, while veins transport de-oxygenated blood back to the heart. Most blood is pooled in veins, which means it's likely to collect. As a result, veins need valves to prevent the backflow of blood. This contrasts with arteries, which are thick, strong and able to withstand the high pressure the heart demands.