* Stretching between two bodies of water: The Caucasus Mountains stretch between the Black Sea and the Caspian Sea.

* Northern border of Muslim lands: Historically, the Caucasus Mountains have served as a natural boundary between various cultures and religions. While the northern Caucasus region is predominantly Christian (particularly Russian Orthodox), the southern Caucasus region is predominantly Muslim (with a mix of Sunni and Shia Islam).

It's important to note that:

* The Caucasus region is diverse: There are numerous ethnic groups and religious communities within the Caucasus, making generalizations about its entire population difficult.

* Borders are not always clear-cut: The lines between different religions and cultural groups are not always distinct, and there are many Muslim communities in the northern Caucasus and Christian communities in the southern Caucasus.

Therefore, while the Caucasus Mountains have historically served as a dividing line between predominantly Christian and Muslim regions, it's essential to acknowledge the complex and diverse nature of the region.