I am somewhat confused in my first read-through of the rules. I have purchased Roman Early Imperials, but I am having trouble classifying them; my knowledge of the Ancient Period for wargaming is non-existent, this is my first foray into the period, and that may have a lot to do with it.
24 Legionary Romans would be Heavy Infantry, in three ranks? Yet in the rules I see examples of Romans five deep! Are formations containing more than 24 models simply wider. i.e. same depth but of greater frontage?
Imperial Roman legionaries would definitely be heavy infantry in three ranks in normal (combat) circumstances. I suspect your images of Romans which are pictured deeper are in a march column formation for faster movement. If you want to make the units larger then probably yes, i'd make them wider rather than deeper - or even start a new unit!
Auxilia, hmm tricky one, I guess it depends how you think they fought, personally I've always thought they fought like lesser trained/equipped legionaries then i'd have them three deep just like the legionaries. If you reckon they were more lightly equipped than this and were primarily missile troops then i'd have them as 2 ranks deep. Have you noticed the Early Imperial Roman army list on p176 of the rulebook? That's got some useful ideas and suggestions in it, otherwise do feel free to shout up any other bits you get stuck with.
Hope this helps, and we'd love to see pictures when you get some finished! Mike
I think that the problem is a little more basic than that. Yes, Mike is right about the formation, but this is a game and the basing requirements can influence the formations greatly. IF you base everything individually, you will get total flexibility on formation, but it becomes rather tedious when moving them about a tabletop. In HC, while there is no need to rebase and most use WAB basing for their existing armies, some will use their individually based figures on movement trays, which can dictate the formation. Others will have based their armies using the same basic WAB formula of 20mm per foot figure, but place four figures on a base (this is what I have done). This gives you a 24 man cohort on 6 bases, which is another suggestion in the rules for the units. It gives you a fair amount of flexibility and you don't have as many individual bases to move around. However, with four men to a single base, 6 bases will give you a line of only two ranks or a phalanx of 4 ranks. At the end of the day, you go with what suits you best, or what your regular opponents are using. HC is concerned with units and basic unit size rather than numbers of figures. Formation has an influence as well, because there are rules for units in different formations, penalties and advantages. Page 16 goes into unit sizes and page 18 onwards explains formations. In the Shooting and Combat rules you will find the appropriate modifiers for units in certain formations as well as some additional rules in the section headed "Useful Rules".
The other thing is that the photos used in the book are mostly for aesthetics and some figures probably looked better arranged in units with five ranks. If you look carefully, you may find that some of them have been placed on some rather nice and elaborate "movement trays" or display stands. They weren't photographed to show them off in a typical fighting formation.
If it helps i've based my heavy infantry 6 to a base, three deep and two wide - 60x40mm, as they are usually standard units of 24. I felt basing them like this made sense as I could put them into a column if i wanted to, and I would probably never need to deploy them any deeper, and would only have to move 4 bases to move the whole unit. Archers I kept on 40x40 so their 24 men can either occupy a longer line than the heavy infantry, or so i could use fewer of them to make up a unit with the same frontage. Skirmishers are on 50mm round bases because I think they look better this way, more like a 'cloud' of troops than a regimented line. My current plan is to model a 'standard' warband units as around 32 figures on 6x50mm square bases with more models on the front three bases so it looks less regimented than the other formations. I realise this is slightly out of the remit of your original question, but i thought explaining it might give you some insight into my own thinking on the subject!
Welcome, Erosthenes! Hail Caesar was designed to be much more flexible and less proscriptive than many other Ancients rule sets. Therefore players have a great deal more freedom to create units that look 'right' to them. So whether your legionary heavy infantry units are two or three ranks deep is really up to you. Likewise with spear-armed auxiliary units, which also may be fielded as either medium or heavy infantry, whichever you think best reflects their historical performance.