Testudo and Synaspismos

[D B Campbell]

Arrian actually defines synaspismos, although not by distance, as a density so packed that it is impossible to turn to any side.

This is true (notwithstanding DeVoto's eccentric translation, which cannot be trusted on this point, as on so many others).

I merely point out that Arrian omits the measurements found in the other "tactical handbooks", in case the OP thinks otherwise. And it is worth bearing in mind that, whenever he does supply measurements in connection with the Macedonian phalanx, they do not conform to those of Aelian and Asclepiodotus (see Ancient Warfare VIII.3). So even if we assume that Arrian intended to define synaspismos as strictly applying to a phalanx in pyknos order (and that exactly the same spacing must then apply to the Roman testudo), his idea of pyknos may not have been the same as Aelian's or Asclepiodotus'. (Must the men be standing at intervals of precisely one-and-a-half feet in order not to be able to turn to either side?)