It's not "research" but I found the schiltrom performed well to plug a bridge. I used stakes (backed by swordsmen) to funnell the exit to the bridge. To fill the gap on the road where you can't plant stakes, I placed 3 mercenary spearmen close together in schiltrom formation.

The Danes threw two near full stacks of good troops (mounted knights, dismounted FKs, those armoured pike-type militia etc) against that bridge and lost them all. By the end of the battle, I had lost only 2 spear units (had two spare).

Of course, the longbows helped. But still, I was impressed with the staying power of the schiltrom. They held up against both heavy cavalry and heavy infantry.