Cattāri Brahmavihārā

316. It is just as if a man travelling in a forest should come across an ancient road, an ancient path, traversed by men in former times, and proceeding along it, should come to an ancient city, an old royal citadel lived in by men in former times, with parks and groves, water tanks and walls – a truly delightful place. Then, suppose that this man should tell of his discovery to the king or a royal minister, saying: “Sire, you should know that I have discovered an ancient city. Restore that place.”
Then, suppose that ancient city was restored, so that it became prosperous, flourishing, populous and was filled with folk, and it grew and expanded. In the same way, I have seen an ancient road, an ancient path, traversed by the fully enlightened Buddhas of former times. And what is that path? It is the Noble Eightfold Path.

Samyutta Nikaya II.105