No, Mandarin is a northern dialect that has emerged only over the last five or six hundred years. If you transported a Mandarin speaker to the Sung, we would probably be able to understand court language only with difficulty; to the Tang, not very much.
Let’s make a sweeping generalization: south of the Yangtze China is more mountainous, and north of the Yangtze is flatter. The flatter territory made transportation easier, so people were able to travel hither and yon, so they had to be able to communicate with people from further distances. This ironed out the dialects and made them more homogeneous. The South is more mountainous, so as one of my teachers said, in Fujian there is a dialect for every valley.
Another factor is that invaders leaked into those open spaces, and many people fled south to escape them. Overall, the south is more conservative; probably the most conservative provinces are Fujian, Guangdong, and Taiwan. Again, I am making very sweeping generalizations, but that conservatism slowed language change, too.
So anyway, Mandarin is quite a new dialect. Ancient China means before the unification in 221bce. We wouldn’t be able to understand a word they said, and there are endless debates about the pronunciation of that time. However, if you plunked someone who could read traditional characters today into say around 200bce, they would be able to read the writing.