Simplify the following text for a Grade 8 native English-speaking person.
Original: The line of march was now stretched out perilously long â '' estimates are that it surpassed 15 km ( 9 miles ) , and was perhaps as long as 20 km ( 12 miles ) .
Simplified: The line of march was dangerously stretched out â `` estimates are that it was more than 15 km ( 9 miles ) , and was perhaps as long as 20 km ( 12 miles ) .