What came first horizon or horizontal line?

The concept of a "horizontal line" or "horizontal" existed before the concept of a "horizon." The term "horizontal" is used in geometry and mathematics to describe a line or plane that is parallel to the horizon or perpendicular to the vertical direction (i.e., it runs flat from left to right). The Word "horizontal" has been used in this geometric sense for centuries.

On the other hand, the term "horizon" primarily refers to the apparent boundary between the Earth and the sky as seen from a specific point. The concept of the horizon has been part of human observation and language for much longer than precise geometric terminology. It's a fundamental aspect of how we perceive the world, particularly the natural world.

So, to summarize, the concept of a "horizontal line" came first in the context of mathematics and geometry, while the concept of the "horizon" has been a fundamental part of human observation and understanding of the Earth's curvature for a much longer time.