• Nagara Sutta

The Buddha tells the monks how, before his Enlightenment, he was worried by the existence of birth, old age, decay and death in the world, and how, gradually, he discovered the conditions that caused their coming-to-be and their cessation. Thereupon knowledge arose in him and insight. Just as, when a man, faring through a forest, comes upon an ancient city and announces his discovery to the king, who has the city restored, so did the Buddha see the ancient path traversed by the Enlightened Ones of the past and declare it to many, to devas and to men. S. ii.104 ff.