If you look at the time lines, Ajanta Caves have had this peculiarity of going into a cycle of oblivion for many centuries, over its known history. Ajanta was an active center for many centuries during the Hinayana period of Buddhism. The oldest of the cave was probably excavated in 2nd or 1st century BC. The last of this series, probably a 100 years later.
What happened to Ajenta for another 400 or 500 years is not very clear. It went into an oblivion before rediscovered and patronised by the Mahayana Buddhists. This happened around 4th century CE, though the exact period is still debatable.
Ajanta then went through an intense phase.More than 20 of its caves were excavated during this period. This lasted probably till the end of 7th century CE. This time again, the circumstances for its decline is at the best sketchy.
However there are some patterns, the decline and re-emergence of activities at Ajanta coincided with other political and religious happenings in the region.
So when was Ajanta rediscovered again? About 1000 years after its second oblivion. This time we have a definite date :28 April 1819, to be precise !
How do we know that? The military officer during the colonial period who was on a hunting expedition ran across the arched window of a cave. He did a favor.
Right across the chest of a painted Buddha's image he scored, “John Smith, 28th Cavalry, 28th April, 1819″.
Little did he know at that time that he was vandalizing some of the beautiful ever murals the medieval world has created.
Nevertheless that mark still remains at the on the 13th pillar on the right in Cave 10. Where John Smith stood and wrote his piece os claim was a 5feet rubble that got deposited at the court of this cave over the centuries. That mark now stands about 10 feet high on that pillar.
What happened to Ajanta after the John Smith event is history!
By the way the last cave in this series was discovered as late as 1956.