The self-exercises in CAPVT VIII of Wheelock's Latin (7th Edition) include the following sentence (#11):
Litterās ad virginem scrībit.
He is writing a letter to the maiden.
I'm confused about the use of ad (+ acc.) here. The chapter mentions that ad is used in the sense of "to, up to, near to with verbs of motion", but scrībit doesn't appear to be such a verb. Why do we not use the dative case instead? I would have expected this:
Virginī litterās scrībit.
Are the two constructions interchangeable in this context?