Disclosed are catalyst systems and methods of making the catalyst systems/supports for the polymerization of an olefin containing a solid titanium catalyst component having a substantially spherical shape and containing an internal electron donor, a support made by contacting substantially equal molar amounts of a magnesium compound and an epoxy compound in the presence of an aprotic solvent and subsequent treatment with a halogenating agent to provide a magnesium based catalyst support. The catalyst system can further contain an organoaluminum compound and an organosilicon compound. Also disclosed are methods of polymerizing or copolymerizing an alpha-olefin. The methods involve contacting an olefin with a catalyst system containing the solid titanium catalyst component.