I was watching this documentary on Youtube called 'The Other Land of the Gods' and they mentioned the fact that after the Romans defeated the Thracians (Indo-European tribes who lived in southeastern Europe), they made statues in their honour, and those statues were huge, up to 3 metres tall (that's 10 feet for you americans).
So they asked, what if those statues were made to resemble what actual Thracians looked like? What if they were really that tall and that's the reason the Romans were so impressed by them? They showed a few Thracian bracelets that were too big for a normal human arm, and also a helmet that's too big for a human head. Of course archaeologists have come up with alternative explanations for these objects, but they're ridiculous. For example, they say that Thracians wore the big helmet on top of another helmet. Seriously?
To add to the pile of evidence in favour of this theory, there's the story of Maximinus Thrax, a Thracian soldier who became Roman emperor from 235 to 238. According to ancient sources, he was 250 cm tall (about 8'6'') and enormously strong.
I'm going to try and find more information that could confirm the theory. If I should stumble upon any other interesting story about giants, I'm going to post it here.