The Tunnel of Samos

[BruceH]

It's an interesting article but I'm confused by the bit that suggests determining a right-angle was difficult to do precisely, suggesting the Hero would have used a dioptra.

Surely three straight pieces of wood, length 3, 4 and 5 units, pinned through holes at the ends (the holes being 3, 4, and 5 units apart) would create a right-angle?

And if there is too much flex in the thing, then a double-length base and two triangles would ensure that the right angle was fairly rigid. Or make it bigger. Or both!