It's difficult to say definitively which culture *first* determined the Earth was a sphere, as the concept likely developed gradually over time. However, several ancient civilizations had theories suggesting a spherical Earth, with some even making calculations about its circumference:

* Ancient Greeks:

* Pythagoras (c. 570-495 BC): While his reasoning was philosophical rather than scientific, Pythagoras is credited with being among the first to theorize a spherical Earth.

* Aristotle (384-322 BC): Aristotle provided observational evidence for a spherical Earth, noting the changing constellations as one travels north or south and the curved shadow of Earth on the Moon during lunar eclipses.

* Eratosthenes (c. 276-194 BC): Eratosthenes famously calculated the Earth's circumference using geometric principles and the angle of the sun's rays at different locations. While his calculation was not perfectly accurate, it demonstrated the Earth's spherical shape.

* Ancient Indians:

* Ancient Indian astronomers: Texts like the Surya Siddhanta (c. 400 AD) suggested a spherical Earth and calculated its circumference.

* Ancient Chinese:

* Early Chinese astronomers: Ancient Chinese texts mention a spherical Earth, though their understanding of its shape might not have been as developed as the Greeks'.

It's important to note that early cultures might have had various understandings of the Earth's shape, ranging from flat to round. The concept of a spherical Earth evolved over time, with different civilizations contributing to its understanding.

So, while it's difficult to definitively state which culture *first* determined the Earth was a sphere, the Greeks stand out for their early and well-documented contributions to the idea.