This is called ‘Kshetra palaka Sila’. It is said that this stone slab marched around Sri Venkateswara Swamy Temple for providing security to the shrine at night.
Priests used to keep the keys of the temple on this stone slab every night after closing the temple and take them to open the temple in the morning after saluting it.
A story in circulation tells us that a child falling under this stone slab while it was patrolling around the temple. To avoid recurrence of such mistakes, this stone slab was shifted to ‘Gogarbha Teertham’ which is in the vicinity of the temple and a tiny part of it was kept inside the temple for people to have a look at it.
At present the Kshetra palaka sila in all its radiance and full form is in existence at Gogarbha teertham, while a part of it is found in the temple.
Even to this day, the priests touch this stone slab with key bunch after closing one before opening the temple.
If you wish to have a look at the full form of ‘Kshetra palaka sila’, you have to pay a visit to Gogarbha Teertham after having Lord’s darshan.