How was the Roman army in fact organized during Caesar's campaigns in Gaul?

Question

I'm finding contradictory descriptions about how Roman legions were organized during the Gallic Wars (58-50 BC).

• An appendix on Roman military organization in The Landmark Julius Caesar highlights the maniple and says that there was "no fixed command structure above the level of the maniple"; but the Wikipedia article on Roman legion's says that the Marian reforms organized around cohorts (rather than two-century maniples). Caeser himself mentions maniples a few times in his own text.
• Many sources emphasize the abandoning of the early Republican distinctions among hastati, principes, and triarii by Caeser's time, replacing them with a single form of heavy infantry; but a footnote to the Oxford World's Classics edition of The Gallic War distinguishes standards triarii and notes that the other "two main standards belonged to the chief centurions of the divisions known as hastati and principes”.
• Wikipedia and many other sources state that even the nominal strength of a century was 80 and in practice was considerably smaller; but a footnote in the Oxford Gallic War states that they consisted of 100 men in Caesar's time.

How was the Roman army in fact organized during Caesar's campaigns in Gaul? Would the following figure be an accurate representation? If so, what role did maniples play?

Answer 1

It is clear from the Gallic Wars and the Civil War that cohorts were both the administrative and the tactical units Caesar and his contemporaries counted in. See for example the first, second and 26th sections of Book 3 So if they wanted to divide their armies, leave garrisons or initiate an attack, they sent cohorts.

But when maniples are referenced, it becomes visible that they still existed as a formation of men marching on the field, and also as an unit of cohesion between the soldiers.

For example in section 76 of book 1 on the Civil War, the general courts the wavering soldiers by maniples, or in section 34 of book 6 on Gallic Wars, when discussing the dangers of countering guerilla warfare in forests, Caesar lets drop that the units gathering around single standards were still maniples.

I am uncertain about the nominal size of the centuries, but in section 69 of the Alexandrine War it is made clear that some veteran-legions were extremely understrength. Even under one thousand, although this is an extreme case enough to be written on.