Castles constitute the most abundant group of Byzantine remains in Anatolia, and offer historians and archaeologists the opportunity to more fully understand both Byzantine settlement patterns and defensive systems through the ages. However, due to their inaccessibility, lack of distinctive construction techniques, and an absence of evidence for secure dating these monuments have often been neglected by Byzantinists. At the same time, historical sources of the eleventh and twelfth centuries make it clear that the Komnenian emperors Alexios, John, and Manuel all engaged in extensive fortification activities. This thesis seeks to critically unite the historical and archaeological evidence for Komnenian fortifications, with the goal of further understanding the Komnenian defensive strategy and evaluating its results. Following a historical overview of Turkish settlement in Anatolia and the Byzantine response, forty Komnenian castles are surveyed, half of them historically attested and the other half assigned to the period based on historical likelihood and, where possible, stylistic similarities with known Komnenian fortifications. The conclusion argues that while the Komneni were generally successful in dealing with the Selçuks diplomatically, they were unable to solve the problem of the nomadic Türkmen, against whom their fortification program was overwhelmingly directed.