Battle Tactic: Baited Detour Gambit
You can use peltasts or cavalry (peltasts are preferable) to lure the enemy away from critical buildings and toward those which are expendable, or even dangerous to the enemy.
This will buy time for prefectures and ballista to erode their strength. When being fired upon, enemy troops will often ignore other targets until they rid themselves of the threat. By dispersing your javelins into open row order, or directing them against a rapid succession of enemy units, you can induce a great many enemy troops to follow your peltasts toward ballista, toward concentrations of Prefects and prefectures, toward your forts or waiting legions, or even back out of your city, and along the wall for the Death Row ploy.
Alternatively you can lead them around in circles over rubble, or into relatively vacant areas. It requires that the javelins closely shadow and pick off enemy troops and flee from pursuit, over and over again.
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See also: Death Row