I think the cataphracts can last longer in melee thnx to their maces.If i had to choose between a cataphract unit or knights to endure heavy melee id have to choose the cataphracts.Oh and if your talkin about Rome total war cataphracts,the differance between them and knights would be the fact that they were covered in armour from head to toe.Just read the accounts of carhae,the ultimate calvary force.I wonder when they adopted the mace?Anybody know?