Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

The people, later to be known as Frisii, began settling in Frisia in the 6th century BC. According to Pliny the Elder, in Roman times, the Frisians (or rather their close neighbours, the Chauci) lived on terps, man-made hills.
The Frisia was named for whom?