Henry Petroski traces the history of bridges in the Mediterranean region and how they evolved over time. A double bridge was built from the town of Abydos, with each of the bridges presumably consisting of boats tied together. Phoenicians employed ropes made from flax on one and Egyptians using papyrus on the other. Floating bridges are no longer very common in an age of high-profile signature structures that also allow for high clearances, but they continue to be used in locations demanding long crossings over deep water, where the construction of foundations and piers would be dangerous and expensive. Two examples of these deck designs exist in the pair of world-class suspension bridges that span the Bosporus at Istanbul and provided the first fixed crossings between Asia and Europe since Xerxes' pontoon bridge across the Hellespont.