Formation Depths?

[Sardaukar]

Adrian Goldsworthy says in his book about Roman army that generally better trained and experienced troops could fight in more shallow formation, since their training & experience compensated the lack of moral support that more ranks gave. I'd say that they still never fought with less than 4 ranks, if they could avoid it.

Pompey in Pharsalus formed his legions in more than usual deep ranks, probably because majority of his troops were inexperienced.