I authored the 8-volume Synagoge, which provided a systematic account of Greek geometry.
I developed the classification of problems as linear, plane, or solid...dependant on their solution by ruler/compass, conic sections, or higher-order curves.
I presented a careful analysis of the classical problems of squaring the circle, trisecting an angle, and duplicating the cube.
Other mathematical ideas I played with are the projective invariance of the cross-ratio of four collinear points, the focus-directrix properties of the conic sections, and the calculation of volumes using rotating planer figures.
One author claimed that on my death, "creative work ceased in the now exhausted field of Greek geometry."
Pappus (circa 290 - 350)