 Later glass roofs such as that of the Grand Palais in Paris employed wrought iron or steel.Other domes and roofs were built using extensive cast iron structures, with cast iron beams used to support the pyramidal roofs of the Palace of Westminster (1840s-50s), and an elaborate cast iron frame for the dome of Saint Isaac's Cathedral in St Petersburg (1837-38).The most famous example is the United States Capitol dome, built 1855-66, entirely made of cast iron, painted to look like stone.