Via dei Fori Imperiali is a strange, brilliant accident: a road Mussolini bulldozed straight through the imperial fora to march armies down, which now serves as the best archaeological promenade in the world. Walk it from the top and the city's whole ancient core unrolls in front of you, ending at the Colosseum.
Begin beside Trajan's Column, the spiral comic strip of a Dacian war, with the brick tiers of Trajan's Market climbing behind it. Then take the avenue itself — and time it for an evening or a weekend, when the road often closes to cars and you can walk down the middle of it. The Forum of Augustus rises on your left, three columns and a great firewall of tufa; the Roman Forum opens on your right, free to read from the railings.
The road points you straight at the Colosseum, which is how it should be met. Lap the outside before you decide about going in. At dusk it glows, the crowds ebb, and Colosseo on Metro B is waiting at the kerb.