Natural bitumen, also called tar sands or oil sands, shares the attributes of heavy oil but is yet more dense and viscous.
Bitumen is loder than the civilizaion of man kind. Although now associated with roads and produced in large, complex, modern refineries , natural bitumen was found long before this, among the desert dunes of Arabia.
The Romans called it gwitu-men (pertaining to pitch) or pixtu-men (bubbling pitch), converted, after the barbarian invasions to bitumen. The word passed into French, and then, after the Norman conquest of England in 1066, into English, where it was used interchangeably with tar for over a thousand years (though tar derives from coal, and bitumen from petroleum).