Which was the greatest Flat horse ever?

Which was the greatest Flat horse ever? Any discussion of which was the greatest ‘anything’ ever is, invariably, biased towards events occurring in the recent past. Furthermore, ‘greatest’ is a subjective term, not necessarily based on empirical evidence, so which was the greatest Flat horse ever is really just a matter of opinion. Notwithstanding the fact that Timeform ratings were not published until 1948 and, for much of their existence, included only horses that raced in Britain, they probably provide as reliable a comparison between generations as we’re likely to find.

According to Timeform, the greatest Flat horse ever was Frankel, who won all 14 of his races between August, 2010 and October, 2012, including ten at the highest, Group One level. His Timeform Annual Rating of 147, achieved when winning the Queen Anne Stakes at Royal Ascot in 2012, is 2lb higher than that of Sea-Bird, who raced just once in Britain, but was an effortless winner of the Derby at Epsom and the Prix de l’Arc de Triomphe at Longchamp in 1965. Of course, there are numerous Flat horses that never raced in Britain, or did so before the advent of Timeform, that could described as the ‘greatest’ ever; Secretariat, Phar Lap and Pretty Polly are just three of them.