Travis Jacobs, Steve Douglas, and Matthew Raymer at [Ad Hoc] Christianity have posted another round-up of biblical studies and theological blogging. In their podcast, “Episode #18: Blogosphere roundup, May 4, 2011“, they discuss a large number of blog posts over the last few weeks, including one from Remnant of Giants which was titled, “The Height of the Giants who survived the Flood“.

They also (and I speak in the plural, because I’m not sure if it was Travis, Steve, or Matthew) ask a question about the height given for Achilles, Ajax, and Orestes. Their height was depicted in this graphic art by homoerotic artist, He Thong:

In answer to your question, these statures appear in Heroikos, by Philostratus of Lemnos:

In his work Heroikos (“On Heroes”, ca. AD 230), the sophist Philostratus the Lemnian  addresses the general belief that ancient heroes averaged more than 10 cubits – equivalent to more than 4 meters or 12 feet – in height. Philostratus mentions, as an empirical evidence for giant heroes, the findings of  enormous bones in the places where the heroes’ tombs were traditionally assumed to lie.
On the basis of the sizes of those bones, Philostratus states that, for instance, Orestes – one of Agamemnon ‘s children – reached 3 meters or 10 feet; Ajax – king of Salamis and a principal character in Homer’s Iliad – was not less that 4.5 meters or 15 feet tall; and Achilles – the greatest warrior of the Trojan war, according to Homer – was a colossus 10 meter or 33 feet in height.
– He Thong
 So, this particular tradition concerning the height of Achilles, Ajax, and Orestes is quite late, from the end of classical antiquity – although Philostratus is reporting a belief about the height of these heroes which was already in existence in the early third century AD.