Albert Barnes Commentary 2 Kings 19:32

"Therefore thus saith Jehovah concerning the king of Assyria, He shall not come unto this city, nor shoot an arrow there, neither shall he come before it with shield, nor cast up a mound against it." — 2 Kings 19:32 (ASV)

Nor come before it with shield - The shields of the Assyrians are very prominent in ancient sculptures and were crucial in a siege. Attacking archers were usually defended by a comrade who held an enormous shield before them both as they shot their weapons. This shield was made of a wooden frame, filled in with interwoven branches, and perhaps lined with skin. It rested on the ground, generally curved backward at the top, and was usually slightly taller than a man. From the safe shelter provided by these large defenses, the archers could take deliberate aim and fire their volleys effectively.

Nor cast a bank against it - Mounds or banks were among the most common methods the Assyrians used against a besieged town. They were piled up against the walls and consisted of loose earth, trees, brushwood, stones, and rubbish. Sometimes the mound's surface was paved with several layers of stone or brick, forming a solid road or causeway capable of supporting a great weight. The goal was not necessarily to make the mounds level with the top of the walls, but rather to raise them high enough for the battering ram to work effectively. Walls were built very solidly at their base to resist the ram, but their structure was comparatively weaker and thinner halfway up. Therefore, the attackers' siege engines, such as rams and catapults, were far more effective if they could strike the upper, weaker part of the defenses. The mounds were raised for this very purpose—to enable them to reach these sections.