Five centuries before the Pilgrims landed in Massachusetts, indigenous North Americans had already built a vast urban center on the banks of the Mississippi River where East St. Louis is today. This is the story of North America's largest archaeological site, told through the lives, personalities, and conflicts of the men and women who excavated and studied it.   At its height the metropolis of Cahokia had twenty thousand inhabitants in the city center with another ten thousand in the outskirts. Cahokia was a precisely planned community with a fortified central city and surrounding suburbs. Its entire plan reflected the Cahokian's concept of the cosmos. Its centerpiece, Monk's Mound, ten stories tall, is the largest pre-Columbian structure in North America, with a base circumference larger than that of either the Great Pyramid of Khufu in Egypt or the Pyramid of the Sun at Teotihuacan in Mexico. Nineteenth-century observers maintained that the mounds, too sophisticated for primitive Native American cultures, had to have been created by a superior, non-Indian race, perhaps even by survivors of the lost continent of Atlantis. Melvin Fowler, the "dean" of Cahokia archaeologists, and Biloine Whiting Young tell an engrossing story of the struggle to protect the site from the encroachment of interstate highways and urban sprawl. Now identified as a World Heritage Site by UNESCO and protected by the Illinois Historic Preservation Agency, Cahokia serves as a reminder that the indigenous North Americans had a past of complexity and great achievement.