Trajan's Markets in Rome is often called the world's oldest shopping mall. But the curved brick complex beside Trajan's Forum is also a giant retaining wall, built into the cut-back slope of the Quirinal Hill.

• ✓Museo dei Fori Imperiali / Mercati di Traiano official site (nodes 6885, 6917, 6920)
• ✓Cassius Dio 68.16.3
• ✓it.wikipedia "Mercati di Traiano"
• ✓Wikipedia "Trajan's Market"

These brick shops in Rome are built straight into the side of a hill. This is Trajan's Markets, called the world's oldest shopping mall. But that's not why it's here. Nineteen hundred years ago, Emperor Trajan wanted a huge public square, his forum, right here, but a hill was in the way. So his builders cut into the hill, and needed a way to stop the cliff from sliding into the square. Their answer: more than a hundred and fifty brick rooms, stacked six levels high, pressed against the cliff. Many have the wide doorway of a Roman shop: one room, open to the street. Shops or not, the whole building is really a giant wall, still holding back that cliff. Subscribe for a fact every day.