"I had a skimpy little toga that reached to my knee, with a Roman belt around it - what they called a zone."

The toga was a bulky garment (made from up to 6 metres of fabric) worn by Roman men; Nan's costume would probably be better described as a tunic.

A tunic was a light, short sleeveless garment cinched at the waist with a belt.

The belt (known as a cingulum) was an important item of Roman men's clothing; it was often very ornate and might have various items attached to it, including weapons in the case of soldiers. A zone is an archaic word for a belt or girdle.

 

Reconstruction of a Roman centurion's cingulum
GNU Free Documentation LicenseReconstruction of a Roman centurion's cingulum - Credit: Wolgang Sauber, Wikimedia Commons