Ptolemy was not the originator of the geo-centric model, rather, he was the one who developed the most sophisticated version of the geo-centric model. His model was one of essentially wheels turning on wheels with the Earth sitting inside of the smallest wheel:
Each planet appeared to move on an circle known as an epicycle whose center connected to a larger circle known as the deferent. This convoluted construction lead to retrograde motion as:
The model although cumbersome (and silly by today's standards), served its purpose in that it was consistent with the observations and physics of the day.