The new Genoa bridge

The City Reunited Edward Glaeser ities have long been the nodes of the network that connects our world. As boats provided the best means of moving long distances throughout most of human history, water flows through almost all older urban landscapes, just as the Polcevera flows through western Genoa. Yet while water is a boon to long distance travel, it is a barrier to shorter trips and so bridges provide the bond that ties cities together. When a great bridge falls, it tears the city apart. When a bridge rises again, as it is rising again in Genoa, that symbolizes the resilience both of the city and the human connections that all cities enable. Romans were the first great bridge builders of the west, justly famous for extraordinary structures that once crossed the Danube and still span the Guadiana. But these largely military bridges were far less important for daily life than the urban bridges that crossed the Tiber and the Seine. Those structures enabled the cities of Rome and Paris to expand and welcome new populations, such as the immigrants from the east who came to Trastevere even before Augustus turned a city of brick into a city of marble. The water that surrounded Rome’s hills and the island of Lutetia served as much for defense as for trade. The earliest Roman bridges, such as the Pons Sublicius, provided only a narrow entry into the city that could be destroyed or defended by legendary heroes like Horatius. As Rome’s military success became more absolute, water’s military importance receded. The city’s bridges servedmore to defend against plague than against Etruscans attackers. The singlemost important task facingall city governments is toprovidecleanwater.Nocrimewave kills asquicklyas acholeraepidemic. Thebeautyof the Pont duGard isonlyenhancedby the fact that it carried life-preservingcleanwater rather thanoxcarts. Rome’s urbancivilizationwas kept aliveby its aqueducts. GreatAtlanticport cities, suchasBordeaux, Buenos Aires, Liverpool andNewYork,wereoften located at theplacewhere the rivermeets theoceanso that river-bornegoods fromthe interior canbe loadedonto long-distance ships.Genoaalsohas a river andafine natural harbor, but thePolceverawasnever amajor tradeconduit.Mountains limitedGenoa’s connections to itshinterland, and thegreat Po river systemflows to theeast and theAdriatic. Genoa grew great not by connecting its own countryside with the outside world, but by building amuchwider mercantile empire that extended from Constantinople to Bruges. The harbor helped, but Genoa’s commercial triumph owed far more to its human capital and entrepreneurial institutions. C 17

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