The statue was constructed of bronze plates over an iron framework (very similar to the Statue of Liberty which is copper over a steel frame). According to the book of Pilon of Byzantium, 15 tons of bronze were used and 9 tons of iron, though these numbers seem low to modern architects. The Statue of Liberty, roughly of the same size, weighs 225 tons. The Colossus, which relied on weaker materials, must have weighed at least as much and probably more.
Ancient accounts tell us that inside the statue were several stone columns which acted as the main support. Iron beams were driven into the stone and connected with the bronze outer skin. Each bronze plate had to be carefully cast then hammered into the right shape for its location in the figure, then hoisted into position and riveted to the surrounding plates and the iron frame.