Why did the oval shield replace the scutum?

[Sean Manning]

Xenophon repeatedly tells in the Cyropaedia (eg. 4.2.22) that his fictional Persians were armed with gerron, thorax, and either sagaris (an Iranian or Scythian axe) or machaira (a chopping sword). They fought in ranks and files with about a square yard of space per man. I believe that the military scenes in the Cyropaedia are supposed to instruct Greek readers, so clearly he believed that men armed "like the Persians in pictures" could behave similarly to Greek hoplites. Whether his fictional armament was ever seen in real life is another question!

But the "gerron" doesn't necessarily mean a taka, it could also be a spara. Also, in Xenophon's Cyropaedia Persians are merely Spartans with eastern names and clothes.

In context, its clear that he means smikra gerra (the round or crescent kind about 60 cm across which was common in Anatolia). This matches the vase paintings which he helpfully tells us his warriors resemble (Cyr. 1.2.13), and he makes the point that these shields were less protective and less useful in pushing than the Egyptian body shields. His comments about the strengths and weaknesses of different armaments agree between his fiction and non-fiction works.

The Persian gentlemen in the Cyropaedia are a fictional community of Xenophon's ideal gentlemen; there is certainly Spartan influence but the military lessons are ones which any kalos kagathos could learn from (Xenophon had some doubts about how the Spartan system worked in practice!)