In middle centuries, the Muslims with a dynamic civilizational foundation had a great influence on other civilizations, especially in the Western Christian society. These impacts have been carried out in various ways and different regions, one of the most important of which is Andalusia, especially its frontiers. The relations between Muslims and Christians, either in conflict or peace, have been widespread within these borders. The outcomes of these relations have been considerable on both sides in military, social, cultural, and economic fields. Since the Muslims have been superior in different aspects over the Western Christians, the influence of the Muslim Civilization has been very considerable in terms of the frontiers of Andalusia. While examining the term thaghr (frontier) and the words related to it, this article seeks to answer the question as to what other functions these frontiers have had besides defense. The hypothesis in mind is that besides defense, the frontiers have had other functions such as cultural, political, and economic as well, which have been due to the widespread contacts between the Muslims and Christians in the frontiers’ regions.