Describe the difficulties posed by some primary sources as a record of history after reading one of the selections from Virgils Aeneid. Although it is a primary source, why can we not blindly take it as an unequivocal fact?

Read: http://classics.mit.edu/Virgil/aeneid.1.i.html

Describe the difficulties posed by some primary sources as a record of history after reading one of the selections from 
Virgil’s Aeneid. Although it is a primary source, why can we not blindly take it as an unequivocal fact?