The height of roman soldiers

The ideal height for a Roman soldier was 1 meter and 77 centimetres (5,8 feet); to be a member of the first cohort the legionnaires had to be minimum 1 meter and 72 centimetres (5,6 feet), according to the ancient historician Vegezio.
These rules were not strictly applied,  in fact historical documents of the fourth century show that in the chosen units of the Roman army there were soldier even 1 meter and 65 centimetres tall (5,4 feet). In Pompei archeologists found a soldier who was 1 meter and 70 centimetres tall (5,6 feet).
Historical sources tell us that all the soldiers in the Nero's Legio I Italica were at least 1 meter and 77 centimetres tall (5,8 feet).
Noteworthy is the discovery of a soldier, perhaps enlisted among the people of the Frisi, who was 1 meter and 90 centimetres tall. (6,2 feet).

Bibliography: The Roman army by Chris McNab