The oldest of the Ajanta Caves dates to 2nd century BC, coinciding the Satavahana dynasty period.

Of the 30 caves, 6 caves (caves 8,9,10,12,13 and 15A) were executed during 2nd to 1st century BCE. Ajanta was an active center of Hinayana period of Buddhism, wherein Buddha was worshipped in an aniconic/symbolic form.

First oblivion

What happened to Ajanta for another 400 or 500 years is not very clear. Probably it went into an oblivion before rediscovered and patronised by the Mahayana Buddhists. This happened around 4th century CE.

Resurgence & decline

Ajanta now gone through an intense phase. Mahayana Buddhists excavated more than 20 of Ajanta's 'modern' caves. Some old caves were reused. This series of cave excavation lasted probably till the end of 7th century CE.

Unlike the Hinayana school, the Mahayana worshipped Buddha in an icon form. The famous mural paintings of Ajanta were done during period. So was the sculptural work with images of Buddha iconography dominating the artistic themes.

The decline and re-emergence of activities at Ajanta coincided with the political and religious happenings in the region. The circumstances for its second decline is at the best speculative.

Ajanta was abandoned and forgotten, once again.

Re-discovery

About 10 centuries after its second oblivion, Ajanta was re-discovered ( again!).
This time we have a definite date: 28 April 1819

A military officer during the colonial period was on a tiger hunting expedition, stumbled across the arched window of a cave. Curiosity took him into the cave with help of local shepherds.

He did a favor to himself after entering the cave. Right across the chest of Bodhisattva's image he scored, “John Smith, 28th Cavalry, 28th April, 1819″.

Little did he know that he was inadvertently vandalizing one of the most beautiful murals the medieval world has ever created. Nevertheless that graffiti still remains on the 13th pillar in the Cave 10.

Many ask how could he make a graffiti 10 feet up on the pillar. Where John Smith stood and wrote his piece of claim was a 5 feet rubble that got accumulated over the centuries.

What happened to Ajanta after the John Smith event is history!

By the way, expeditions, re-discoveries and exacations kept happening. The last cave in this series was re-discovered as late as 1956.