This is a rare geological arch and the only one its kind in the whole of Asia.This is one of the rarest geological faults in our country and the age of the rock is estimated at 2500 million years and the age of the arch around 1500 million years.Two other such arches are known to exist in the world today: The Utah Arch in the USA and the arch cut through the del radian quartzite of U.K. Its length is 25 ft and height 10 ft. Devotees believe that Lord Venkateswara the presiding deity of this sacred hill appeared through this as Swayambhu and took his abode at the temple which is just a kilometer away. Hence the name Sila-Thoranam or idol-entrance. This place has been beautifully developed as a tourist spot with nice greenery gardens plants and trees. It is truly enchanting. Most pilgrims coming to Tirumala are unaware of these tourist spots.