WHY WAS DHUL-QARNAIN CALL "OWNER OF TWO HORNS?

THIS is a controversial issue,that there is not a definite known reason behind this. some said: he had something on his head that looked like two horns.
wahb ibn munabih said:he had two hormns of brass on his head.(This interpretation is very week)
some schoolars from among the people of book (christian and jews) said: This is becouse he ruled over persion and roman territories. it was also said:that he reached the fisrt ray of the risung sun on the east and that on the west and he ruled over all that was in between.( The letter opinion is more likely true,which is the saying of Azzuhuri.
(Ibn katheer stories of qur,an pg:129)