CHAPTER 1 5 CROSSING AND CONNECTING Twelve year old Jin stands in line with his family He is waiting for his turn to walk across the Zhangjiajie Grand Canyon glass bridge in China The bridge is made of 99 glass panels Each has three layers and can support 40 tons 36 metric tons Finally it's Jin's turn to cross the amazing 1,400 foot 430 m bridge Tourists walk across the Zhangjiajie Grand Canyon glass bridge
6 Jin watches as some visitors hold the railings Others crawl on their hands and knees But Jin walks bravely across He can see the 1,000 foot 300 m drop beneath his feet Bridges are structures people use to get across a river road or other obstacle Bridges are built in different ways depending on the climate terrain and materials available A bridge can be a simple piece of rope Or it can be a complex structure of towers and cables The ancient Romans were among the first to show their skills in bridge building Their bridges had arches made of stone But they needed to make
7 The Romans built this bridge in Cordoba Spain during ancient times the bridges stronger and sturdier By 2 BCE they had discovered how to make waterproof concrete Using a cofferdam they could make a concrete bridge The ancient Chinese also built bridges They used wood stone bamboo and iron chain
