While there was a lot of awe and stopped soldiers while the attacks rained down from above, there were also many undead moving. From what the archers could spot, many undead had emerged and begun to look for the source of the attacks. There were also undead that used spells to create places with dark shields.
The dark shields were a skill that Gil and the rest of the party had seen before. Dark wall was something that the darkness mages were able to use to block many attacks. It used darkness mana and their own shadow to make a wall that defended them. The fact that the undead mummified priests could use it was to be expected.
What Walker could see as he had descended was also the rising quality of the undead. He did not spot many of the lesser mummified priests and only saw groups of mummified priests. That also meant to him that there would be many more high ranked undead when the soldiers tried to invade the massive central building.