Why were officers posted to positions behind the lines during each battle

they where posted behind the lines during each battle because behind the trenches and lines their were shops command centers and other stuff so officers and soldiers had to stay by the trenches because they had to fight and they shouldn't just be walking around.  

Explanation: this is the answer I done this question before its not word for word but this is really close.

how did justinian contribute to the byzantine empire?

one famous byzantine emperor was justinian i. justinian ruled from ad 527 to 565. belisarius was the commander who led these armies in an attempt to win back the old western roman empire. the war effort to take back the western part of the empire forced justinian to raise taxes on the people of the byzantine empire.

explanation:

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a system of cooperative federalism emerged, as the powers of the federal government expanded.