SN 12.65 Nagara Sutta: The Ancient City
The Buddha gives an account of his discovery of dependent origination and gives this simile:
Suppose a man wandering through a forest would see an ancient path, an ancient road travelled upon by people in the past. He would follow it and would see an ancient city that had been inhabited by people in the past, with parks and groves, ponds and ramparts, a delightful place. That man would inform the king and suggest that the city be renovated. The king would then do that and the city would become successful and prosperous and well populated. So to, bikkhus, I saw an ancient path travelled by the perfectly enlightened ones of the past. What is that path? It is this Enobling Eightfold path.