Roman Shieldwall or testudo?

[Nathan Ross]

The testudo is not the same. Robert is correct when he said that it was usually only used during sieges.

While the classic shed-like formation depicted on Trajan's Column might have been used mainly in sieges, the word testudo apparently had a wider application. The Phillip Rance paper that Robert linked above has this note (p.300):

"The usage of the term testudo was more flexible than is often supposed; as early as the first century A.D. testudo… might be broadly applied to any compact, well-shielded formation in the field, outside the sphere of siegecraft traditionally associated with these terms. The more frequent occurrence of battlefield deployments that explicitly resemble a testudo from the early third century reflects gradual changes in the deployment and tactics of Roman infantry."

Rance goes on to cite examples from Cassius Dio, Zosimus and Ammianus Marcellinus. The problem is that we don't know from the literary descriptions how closely these formations 'in the form of a testudo' might have resembled the one shown on Trajan's Column. Ammianus's troops at Strasbourg 'covering their heads with a barrier of shields' sounds very similar though.