shield wall

noun3

1. •
   A barrier.
2. •
   (historical) A defensive formation, used from antiquity through the early Middle Ages, in which soldiers stand shoulder to shoulder with their shields overlapping, creating a continuous barrier against enemy attack.
3. •
   (figurative) An impenetrable barrier.

   • Their spears protruded from the chinks in this formation that was known as the ‘shieldwall’ or ‘war hedge’. — 1999