These spearmen lack armour and while able to hold the battle line are not the equal of their heavier cousins. They are best used when their flanks are protected.
Sarmatian Spearmen are raised from settled groups of formerly nomadic Sarmatians such as the Siracae of Ciscaucasia. As they abandon their traditional way of life as nomadic herdsmen, more and more of their warriors become infantry. The equipment of these troops reflects substantial Greek influence, which is quite evident in, for example, the large oval shields of the thureos type that these infantrymen carry. That shield is typically their only protection. To it, they add spears and short swords for offense. Thanks to their shields, they may face the many archers that their potential enemies are likely to field with some confidence and their spears allow them to fend off the light cavalry that is also common among their foes. They will also hold their ground against infantry similar to themselves. However, truly heavy cavalry, not to speak of quality heavy infantry will get the better of them sooner rather than later.
Historically, by the 3rd century BC oval shields with long spines and spindle-shaped bosses spread and became common into the areas around the north coast of the Black Sea. The whole region had long maintained strong connections with the Greek world and this particular process followed military developments in the Hellenistic world. Infantry men equipped with oval shields and spears became common among the diverse ethnic groups that inhabited the region including settled Sarmatian tribes.