Book excerpt: In the late-19th century, with the advances in technology and the increase in America's economic stature, a new round of fortification building began in the United States and its overseas territories. Locations such as Portland, Boston, New York, Baltimore, Charlestown, Savannah, Key West, Los Angeles and San Francisco were all extensively fortified. This book provides a concise introduction to the design, development and purpose of American coastal defenses in the "modern" era (1885–1950), a period defined by the use of concrete, steel, and powerful breech-loading rifles. It covers the emplacements, weaponry, equipment, and people that defended their country in times of great change and uncertainty.