Final answer:
The Zapotec civilization built Monte Albàn, which was a major city on a flattened mountaintop in the Oaxaca Valley, and served as the Zapotec's capital between 500 BCE and 800 CE.
Step-by-step explanation:
The civilization that built the city of Monte Albàn on a mountain in the Oaxaca Valley was the Zapotec civilization. The Zapotecs established Monte Albán as their regional capital around 500 BCE.
This mountaintop city reached a population of about five thousand people by 400 BCE and grew substantially to potentially twenty-five thousand inhabitants by 700 CE.
The settlement was likely chosen for its defensible position, dominating the surrounding Oaxaca Valley, which was excellent for maize cultivation and supported the development of monumental architecture.
The influence of Monte Albán extended to numerous smaller communities throughout the valley, indicating the Zapotec's significant regional presence and power.