The limestone forming Batu Caves is said to be around 400 million years old. Some of the cave entrances were used as shelters by the indigenous Temuan people (a tribe of Orang Asli). As early as 1860, Chinese settlers began excavating guano for fertilising their vegetable patches. However, they became famous only after the limestone hills were recorded by colonial authorities including Daly and Syers as well as American Naturalist, William Hornaday in 1878. Batu Caves was promoted as a place of worship by K. Thamboosamy Pillai, an Indian trader. He was inspired by the 'vel'-shaped entrance of the main cave and was inspired to dedicate a temple to Lord Murugan within the caves. In 1890, Pillai, who also founded the Sri Mahamariamman Temple, Kuala Lumpur, installed the murti (consecrated statue) of Sri Murugan Swami in what is today known as the Temple Cave. Since 1892, the Thaipusam festival in the Tamil month of Thai (which falls in late January/early February) has been celebrated there. Wooden steps up to the Temple Cave were built in 1920 and have since been replaced by 272 concrete steps. Of the various cave temples that comprise the site, the largest and best known is the Temple Cave, so named because it houses several Hindu shrines beneath its high vaulted ceiling.