The architectural style of India underwent a drastic change after the Turkish conquest. The Sultans and their nobles insisted on having arches and domes and competent Indian masons succeeded in building them. The first surviving example of arch is Balban's tomb, dated 1280, and of dome, Alai Darwaza, dated 1305. It was the change in bilding technology accompanied by the introduction of lime mortar that made possible the change from trabeate architecture to arcuate style. The principle of true arch seems to have been known in ancient India, but somehow large arches could not be made. However, false arches were constructed in ancient times. Use of lime mortar made it possible to waterproof floors and walls for tanks. Thus, it became possible to build tanks and vats such as those needed for producing India's major dye, indigo.