The Augustan Army ; the continuation of the manipel organization

[Nathan Ross]

Why would Fronto write this to Lucius Verus? Does this not imply that there are still manipels in Fronto’s time?

Not particularly - Fronto is quoting Cato, a writer of the 2nd century BC.

Maniples may still have existed as a part of the legion structure in the 2nd century AD - the maniple titles were still used to distinguish the different centuries in the cohort. But the word seems to have been used more loosely by writers as a synonym for legionary troops, long after the maniple ceased to be the principal tactical or administrative subunit of the legion.