H. W. Kaufmann & J.E. Kaufmann 
Fortifications of the Incas [PDF ebook] 
1200 1531

The greatest period of Inca expansion occured during the reigns of Pachacuti (1438 71), Tupa Inca (1471 93), and Huayna Capac (1493 1527). From the mountain stronghold of Cuzco, they subjugated the surrounding kingdoms and territories, absorbing their civilizations and their peoples. By 1525, they dominated much of the west of the continent, relying on fortified strongholds, an extensive system of roads and bridges, and obligatory military service to control local populations. This title takes a detailed look at the development of Incan fortification techniques, and examines how they came to be overrun by the Spanish conquistadors.