As far as I know, there were no large man-made features at the time of the Roman Empire. Most of the boundaries to the north were formed by rivers. Although there was Hadrian's Wall that formed part of Rome's northern barrier, it was quite small - at only 70 miles long, it created a man made border across one of the skinniest points of Britain.
Sahara
The Sahara Desert was the southern border of the roman empire
One physical feature that the Roman Empire completely surrounded was the Mediterranean Sea.One physical feature that the Roman empire completely surrounded was the Mediterranean Sea.One physical feature that the Roman empire completely surrounded was the Mediterranean Sea.One physical feature that the Roman empire completely surrounded was the Mediterranean Sea.One physical feature that the Roman empire completely surrounded was the Mediterranean Sea.One physical feature that the Roman empire completely surrounded was the Mediterranean Sea.One physical feature that the Roman empire completely surrounded was the Mediterranean Sea.One physical feature that the Roman empire completely surrounded was the Mediterranean Sea.One physical feature that the Roman empire completely surrounded was the Mediterranean Sea.
British territory surrounded the globe. there was no western boundary.
The Appalachian Mountains marked the western boundary of British claims.
The physical feature that forms Uruguay's western boundary with Argentina is the Uruguay River. It also forms part of the Brazilian-Argentine border.
Sahara
The physical feature that formed the northeast boundary of Asoka's empire was the Himalayan mountain range.
You decide it is either a natural or artifisial boundry......
Ohio River
The river, Rio Uruguay, borders Uruguay's western border.
A divergent boundary's feature is a Mid-Ocean Ridge if the divergent boundary is underwater.
The Great Wall of China.
The Great Wall of China served as a natural protection for northern China, as it acted as a barrier against invading forces. Additionally, the Gobi Desert to the north provided a natural obstacle that deterred potential invaders.
There are the Rif Mountains, and the Strait of Gibraltar, for two.
Appalachian mountains
some physical features about divergent boundaries are rifts that may turn into rift valleys, and sometimes it may fill with magma