Where did the name “Narnia” come from? What does this name mean?

Walter Hooper, Advisor and Consultant to the literary estate of C.S. Lewis (and avid collector of Lewis artefacts) claimed that the name came from a map that Lewis had as a child, referring to the Italian town of Narni(a). Hooper evidently had the map in his possession.

"It will perhaps surprise you to hear that I spent a day (in Narni/Narnia) in October (1996). In fact, this was my second trip, as my godson and I were there first five years ago. C. S. Lewis came across the name 'Narnia' in a classical atlas he used as a boy, and continued to use it all his life. I have it now, and it's interesting to see that he underscored the name when he first saw it back in about 1914. In Italian Narnia is called 'Narni', and it's under that name that you will find it on modern maps.

_{^{Narnia and Narni}}