Adding fearsome weapons to the unshakable Unsullied makes for a truly unbreakable center to any formation. Despite their armor rating a "light" classification in the western sense, and Unsullied spear wall, advancing in lockstep according to doctrines laid down in the Old Empire of Ghis, can move on virtually any position without fear of counterattack from the flanks or even the rear. While such a formation might seem immune to cavalry, a commander would be wise not to let them march forth unsupported, but if any unit can weather a short-term encirclement, it's the Unsullied Pikemen.