The Romans didn't have phones. However, if they did, what text messages would they have sent?

They most likely would have sent messages like if they won or lost a battle. The modern Athens Marathon commemorates the run of a messenger from a battlefield at the site of the town of Marathon, Greece, to Athens in 490 B.C. Legend has it that a messenger delivered the momentous message “Niki!” (“victory”), then collapsed and died. Maybe messages of where they should meet for battle, so if the figure out the enemy is attacking 50 miles west of where they were they could message their allies to meet there instead.

Explanation:

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.