Just before dawn, the bridges began to fall.One by one, American missiles reduced them to crumpled concrete, strewn across river beds and gorges.For a week, the US had bombed southern cities, cranking up the pressure on Iran to relinquish control of the Strait of Hormuz.But now the US military was going for the transport arteries connecting key southern ports to the rest of the country.The bombings leave Bandar Abbas, a city of 500,000 people where roughly half the country's trade comes ashore, almost completely isolated.