The main difference between a Greek Doric column and a Roman Doric column is that the Roman Doric column has a base. Greek Doric columns typically do not have a base, as they rest directly on the stylobate (the upper step of the temple platform). Additionally, Roman Doric columns may also exhibit a slightly more ornate capital than their Greek counterparts, though the primary distinction remains the presence of a base.
Therefore, the correct choice from the options you provided is:
- The Roman Doric column has a base.