The intersection looks no different from any other here: wide, empty streets, asphalt strips that meet and then diverge again. But it is said that one of the greatest miracles in music history happened here. The intersection was not in the blazing sunlight like today, but bathed in the light of a pale moon when a very young musician, Robert Johnson, took his guitar from his shoulder, laid it in the parched grass by the side of the road, and began to wait.