Ptolemy

Mars's orbit is more elliptical than all the eight major planets except Mercury. This enabled Kepler to discover that the orbit was elliptical and not as previously thought a circle with the Sun offset from the centre (represented by a circle and an epicycle with the centre of the epicycle travelling round the circle, and the planet positioned on the epicycle).

• an epicycle is a system where things rotate around a fixed point.

Venus moved on an eccentric and epicycle, the same as outer planets, but the Center of the epicycle followed the mean sun. Mercury is more confusing, with a crank mechanism that brings the epicycle closer and farther in an ellipse throuout the year, there probably was an Equant too. Venus' model at least was very accurate, and I can't find Mercury's accuracy.

Epicycles helped account for the apparent motion of the other planets in the geocentric model.