The Quincux Formation video explanation!!!

[QuintusSertorius]

look the second video -in the same page-

I saw that, which immediately struck me as "that's not the problem". Gaps in your formation isn't an issue; everyone fought with them because otherwise individual bodies of men would turn into an unwieldy mass that can't be controlled. Only difference was the Romans fought with larger intervals than would have been normal to retain the cohesion of individual formations.

Hell, the Romans developed a looser, more open formation precisely to combat fast-moving Gauls, the idea that it would be a disaster is patently wrong. The Gauls don't swarm in and overwhelm, they're broken up and become disheartened through isolation.

No, my problem is this rather complicated looking movement whereby units disengage, march backwards and shift to one side to place themselves behind other units who are now engaging. I really can't see all that dancing around in contact with the enemy being feasible.