Quote Originally Posted by edyzmedieval
A shield wall is totally different from a phalanx. A phalanx is a mass of 6m spears or iron Sarissa and men, gathered tight, to attack and defend at the same time. A shield wall is a complex "wall" of spears, which is much vulnerable than the phalanx, but much more mobile.
The classical hoplite phalanx used spears of around 2-2.5 metres in lenght as a longer spear would not be managable single handed. Their argive shields, more generall known as hoplons, formed a wall of shields with the spears sticking out from above.
For other shield wall troops the equipment differed of course (armour and of course the shield), but the general idea is the same. Maybe other shield walls were better used in defense (the hoplite phalanx was definitely an offensive formation), but other then that I don't see any principal differences.

Excuse me, but Skoutatoi are after Heraclius' period.
Hmm, then that poses an interesting question: what were they?
Are you sure that the Skoutatoi were developed after his death, or just after his (wildly succesful) campaigns against Persia? After settling peace with the Persians most of the veteran troops were disbanded. Spearmen are relatively easy to train, maybe once the Arabs attacked they started training lots of infantry wich would later evolve into the Skoutatoi...