This makes Sirion a formidable obstacle to an army trying to cross it in the face of opposition and without the further use of the ships of the Telerin fleet the Host of the Valar must fight their way across at those crossings.
This makes Sirion a formidable obstacle to an army trying to cross it in the face of opposition. Without the further use of the ships of the Telerin fleet the Host of the Valar cannot be ferried to East Beleriand flanking the line of Sirion in the south but must fight their way across at one or more of those crossings.