Mo Farah's double gold at London 2012 was the greatest distance running achievement in history, according to his coach Alberto Salazar.
The Briton claimed both the 10,000 and 5,000 metres titles at the Olympic Stadium.
And Salazar reckons the level of competition at the moment means the 29-year-old's feat eclipses those of Lasse Viren, who won both crowns in 1972 and 1976, and Emil Zatopek, who also won the marathon in a long-distance treble in 1952.
"I would say that he did it against better competition than has ever been done before," Salazar told Radio 5 Live's 'Super Coaches' programme, to be broadcast tonight.
"There is clearly no doubt. I know Viren did it twice, I know others did it before that, Zatopek and so forth, (but) distance running now is more competitive by far than it ever has been before.
"It is a much harder thing to medal in distance running now than it was 20 or 30 years ago.
"For Mo to be the very best in the world twice, he's not just repeating or matching what others did that did that double, he's surpassed them by far in doing this."