The most fitting advancement to include in the list of important developments of an ancient civilization, based on the context of the original list, is:
D. Development of the number zero
This is because the development of the number zero is a significant advancement in mathematics, closely associated with ancient Indian mathematics, and aligns with other intellectual and cultural developments such as writing and medical techniques. The other options either pertain to different civilizations or do not fit as closely with the themes presented in the original list.