An Ionic column was a piece of architecture the Doctor's TARDIS disguised itself as, before it was stuck as a police box. (TV: "The Cave of Skulls" [+]Part of An Unearthly Child, Anthony Coburn, adapted from The Pilot Episode (Anthony Coburn), Doctor Who season 1 (BBC tv, 1963).) The Master used to disguise his TARDIS as a Doric column using his functional chameleon circuit. (TV: Logopolis [+]Christopher H. Bidmead, Doctor Who season 18 (BBC1, 1981)., Castrovalva [+]Christopher H. Bidmead, Doctor Who season 19 (BBC1, 1982)., Time-Flight [+]Peter Grimwade, Doctor Who season 19 (BBC1, 1982)., Planet of Fire [+]Peter Grimwade, Doctor Who season 21 (BBC1, 1984).)
Behind the scenes
The shape of the Master's TARDIS on Logopolis is actually a Doric column, contrary to popular belief and its description as "Ionic" in The Discontinuity Guide (see DWM 412). Ionic columns are actually much more ornamented. According to the novelisation of Time-Flight, the Master's TARDIS was Corinthian, although it was still the same shape on screen.