McDevitt, Jack. "The Tomb"
Divergence: 312 CE
What if: Constantine was defeated by Maxentius at the Milvian Bridge, leading to the complete break-up of Rome and a never-ending dark age.
Summary: C. 1700, a young man meets an old man excavating a tomb in a ruined city.
Published: In What Might Have Been? Volume 3: Alternate Wars (eds. Gregory Benford and Martin H. Greenberg), q.v.