Figure 14. Vaults a) keystone causing the thrust in a flat arch b) example of the arch durability (Photos 14.a-b were taken in Hierapolis (Ἱεράπολις), Phrygia, Turkey) c) scaffold supporting an unfinished roof in the Tiryns fortress

From

The World’s Oldest Bridges - Mycenaean Bridges

Karas Slawomir, Nien-Tsu Tuan

American Journal of Civil Engineering and Architecture. 2017, 5(6), 237-244 doi:10.12691/ajcea-5-6-3