From an account by Bartolomeo Fonzio, a professor of literature at the University of Florence in the 15th century:

[S]ome workmen were digging out the foundation of tombs in search of marble on the Via Appia six miles out of Rome. They had destroyed an arch when they came across a marble box.

Opening it up, they found a corpse lying on its face, covered by a layer of fragrant bark two inches thick; all of the inside of the casket was likewise smeared with the same fragrant mixture like some sort of plaster.

When this sweet smelling bark was removed, the girl’s face was as if she had been buried that very day. Her hair, long and dark and firmly fixed to the scalp, was gathered in a knot and divided into twin tresses in girlish manner, all covered by a hairnet of silk interwoven with gold. The cheeks, chin, and throat – you’d think they belonged to a living person.

For days the discovery was the news on everyone’s lips; reports from the time noted that tens of thousands of people came out from Rome to see the incredibly preserved body. Finally, Roman authorities simply ordered the body brought into Rome and put on display.

Despite dozens of theories, we don’t know who she was, since the inscriptions from the site had long since been destroyed or vanished.

As to what happened to her after her unexpected moment of fame in the sun, there are conflicting reports of the body being reburied in secret by Pope Innocent VIII, or simply dumped unceremoniously in the Tiber River.

Via Medievalists.Net.