Which military trend in the later Middle Ages does this formation illustrate?

The image shows dense ranks of foot soldiers bristling with long spears, a “hedgehog” that only works with tight drill and mutual support. Such formations could stop or break charging knights by presenting layers of spear points, shifting the balance of power from individual prowess to collective discipline. Their success depended on maintaining order, depth, and well-timed advances or stands. Pike-armed infantry came to prominence with Flemish militias and especially the Swiss in the 14th–15th centuries, inspiring German Landsknechts and influencing Spanish tercios that later mixed pikes with firearms. This trend eroded cavalry’s battlefield dominance and fueled the rise of professional, paid infantry.