Which achievement is associated with the ancient Egyptians?

The ancient Egyptians are particularly noted for their development of a solar calendar, which was crucial for agricultural and religious purposes, allowing them to track the annual flooding of the Nile and to plan agricultural activities accordingly. Their contributions to geometry were significant, as they needed to measure land for farming and construction, and they utilized geometry in the planning and construction of monumental structures, such as the pyramids. In astronomy, their observations of the stars and planetary movements helped them create a more accurate calendar and informed their understanding of celestial cycles. This skill set not only reflects their practical needs in agriculture but also highlights their sophisticated understanding of mathematics and natural phenomena, marking a highly advanced civilization in the ancient world.

While other options present important historical milestones from different cultures, they do not pertain to ancient Egypt's specific achievements in measurement, time reckoning, and observational science.