The lasting influence of Vitruvius is based upon

a) On Architecture, a seminal work on city planning, construction methods, and the Greek orders.
b) his successful military campaign across the Danube River.
c) a first-hand account of the eruption of Mount Vesuvius recorded in his Letter.
d) his musical compositions and poetry extolling his patron, Hadrian, at the famed Villa at Tivoli.

Answer: a