(05.05 LC)Use the map below to answer the following question:

A physical map of Europe, North Africa, and Western Asia showing major locations within the Roman Empire and its borders around 125 CE. The lowest elevation areas are shaded green and are along the northeastern coasts of North Africa, northern Europe, and the western coast of Spain. The highest elevation areas are shaded light brown and are in southwest Asia, across southern and southeastern Europe, most of Spain, and the northwestern coast of North Africa.
© 2012 Andrein
Creative Commons, Attribution-Share Alike 3.0 Unported

Which of the following best explains why the area between Spain and Gaul was not part of the Roman Empire until 107 CE, even though the surrounding areas were both part of the empire for many years?