Despite how cool this looks, I have only found one (rare) situation in which the testudo is worth using. This is when I am defending a bridge and I surround my side with a U shape line of cohorts so as to surround the enemy as soon as they rush across. If the enemy has archers, I start with all my units in testudo, which allows them to weather the arrows pretty well without having to move from their position near the bridge.

All other situations I have tried the testudo in have been complete failures. Towers on walls seems to kill cohorts as if they didn't have any shields. I find I take less casualties by running my units straight through the area than by slogging through it in slow testudo formation.

Has anyone else had success with this tactic in any other situations?