Several well known ancient civilisations have flourished & declined throughout time immemorial. The Greeks, Romans, Egyptians etc have all declined long ago. Today only one ancient civilisation still survives as the oldest form of philosophy ever known to Mankind on Earth.
Often known as the world's oldest 'religion' Sanatan Dharma is a large spiritual tree which despite having faced several tyrannical invasions, it has managed to survive as well as evolve splendidly whilst managing to keep a firm hold to its Vedic roots. Sanatan Dharma means the Eternal Path.
The secret of its survival into the post-modern era lies within the wisdom of the sacred Divine teachings of the Rishis of ancient BharatVarsh as well as the courage & strength of Hindu warriors who bravely fought against all odds to keep Dharma alive.