Gambesons in roman times?

[Dan Howard]

Scale armour did not form vertical columns like that.

Scale armour aligned vertically, with distinctive lines separating the rows, and pteruges.

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If they were painting scales onto it anyway, why first go to the trouble of carving those vertical bands into the stone?

There is no way to know because we don't have any of these things with the painted detail.

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The relief with the two armoured legionaries shows the lefthand man wearing what is surely mail (incised 'dots'). The righthand soldier is wearing something different - what else would create diagonal bands like that?

No idea. These things aren't photos. The artist may simply have wanted to show two different styles of mail. The only sensible thing to say is that the artist is likely depicting some kind of armour. To say anything more without corroborating evidence is irresponsible.

There is no extant example of textile armour anywhere in the world with diamond-pattern stitching and no textile armour with anything that resembles those dots. Why on Earth would you think it was textile armour?