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The Gobi desert
The physical feature that lies between the Muslim Empire's Northern border is the Caucasus Mountains. These mountains stretch between the Black Sea and the Caspian Sea, forming a natural barrier between the Muslim Empire and the surrounding regions to the north.
roman sa
Andes Mountains.
Colorado River
The Mekong River
The most notable is the Himalayan mountain range.
No!!
none it is entirely artificial
The northern border of the Roman province of Britannia was Hadrian's Wall.
The Caucasus Mountains
The Caucasus Mountains