Mixed masonry of the third century, from the circus of
Caracalla Maxentius near Rome; the surface of the walls formed with alternate courses of triangular and squared blocks of tufo, or peperino; the center of the wall was filled in with rubble.
Vault under the steps of the Circus of
Caracalla Maxentius near Rome, showing a similar construction.
It's along the Appian Way, southeast of Rome. Note the remains of the Tomb of Romulus, the son of Maxentius who died a boy, immediately adjacent the circus.
Circus of Maxentius (Rome: Via Appia, c. 309).