That kinda sounds like a drink order...
From the update:
Lightly armed skirmishers such as these would have been very common in any army of this period. The sling is probably the cheapest an oldest weapon, and with little practice anyone can use one.
Slings often prove more dangerous than a bow as they can knock out or kill a man, even when helmeted. The dress of these figures is typical of the people of Mesopotamia and Assyria.