Upvote:0
I can't give any sources, but think this was only possible after introduction of the scutum (rectangular) shield. Hoplon (round) shields do not make for good testudos. I have never read anything about testudos when the Roman army employed phalanx tactics. Anyway, a phalanx can very well be seen as a form of a testudo.
Upvote:2
Polybius describes the Testudo being used in the capture of Heracleum during the Third Macedonian War, the year was 169BC.
Polybius "Heracleium was taken in a peculiar manner. The town had a low wall of no great extent on one side, and to attack this the Romans employed three picked maniples. The men of the first held their shields over their heads, and closed up, so that, owing to the density of the bucklers, it became like a tiled roof. The other two in succession..."
Source: The Histories of Polybius