Books like Lest Darkness Fall

When am I? Padway asked himself after the lightning-flash knocked him down. He knew where he was--Rome. He was there to study archaeology, and even though the lightning had left him dazed, he could see the familiar Roman buildings. But the buildings looked newer and the crowds in the street were wearing tunics, not suits! And a rich barnyard smell had replaced the gasoline-and-garlic aroma of modern Rome. So, when was he? And he was suddenly cold with fear of the answer...