Which early civilization had a well organized unified empire with an elaborate system of roads covering more than 10,000 miles?

Incas is the correct answer.

Explanation:

Inca Empire existed in modern day Peru and was largest empire in pre-columbian America. It was established by Manco Capac in 1438, it  extended from Quito to Santiago and covered areas of at least 2 million kilometres. Quechua was their official language. One major characteristic of the Incas was that they had constructed more than 30,000 kilometres of roads. Inca civilisation ended in 1532 with the arrival of Conquistadors. They had strong belief in life after death.