Plot Summary:The Great Wall was the Chinese empire's most ambitious investment, attempting to secure its borders (mainly north and west) from nomad attacks by near-impregnable infrastructure. Both building and manning it nearly crippled the treasury, exacting huge financial and human costs in labor, materials and taxes. The engineering was brilliant, adapted in time to match greater challenges, with novel techniques, such as using rice to improve bricks of an industrial 'speed building' size. It had elaborate defenses, including crossbows, battlements and loopholes, traps and mine fields, with extra features and positioning for such purposes as signaling, housing garrisons and moving reinforcements.