segmentata

[Matthew]

In the low middle ages, the sword was the determinant factor of the change of the lorica hamata for the armor of plates, this was equal for the Roman world. The Roman army I look always for the struggle body to body, design his sword short (gladius) for this type of combat, the pilum and the arch were for the alone Roman a support during the fight, but the determinant factor it was recovering always the infantry in the struggle body to body, for the early Roman the cavalry alone I recover a paper(role) of support, I think.

That seems somewhat unlikely. Although Dan places more faith in the protection afforded by Mail than I would (my personal and unsubstantiated opinion is that Lorica Segmenta afforded somewhat better protection and that Mail is penetrable), his contention that you are underestimating the potential of Lorica Hamata to provide protection against all types of weapons seems very possible.
Changes in weapon forms do not necessarily reflect changes in armour and the influence of one on the other is likely much more complicated than simple cause and effect. Furthermore, the perceptons of Soldiers towards the effectiveness of equipment may not necessarily reflect the reality of the situation. One Soldier will swear by one piece of equipment and detest another, whilst another Soldier will have the exact opposite opinion.
The Ancient and Medieval battlefield was a combined arms event and each side provided only what it was politically and economically capable of fielding. Tactics were often subserviant to strategy.
I'm not saying that weapons were never developed to better cope with armour or the that armour was never developed to better resist weapons, but I do think that it is dangerous to identify this as a clear cut reason for the introduction and apparent popularity of Lorica Segmentata, especially when only referring to one particular weapon type that was only a part of those deployed.

At least, that's my view...

Matthew James Stanham