Even as they spoke there came a blare of trumpets. Then there was a crash and a flash of flame and smoke. The waters of the Deeping-stream poured out hissing and foaming: they were choked no longer, a gaping hole was blasted in the wall. A host of dark shapes poured in.'Devilry of Saruman!' cried Aragorn. 'They have crept in the culvert again, while we talked, and they have lit the fire of Orthanc beneath our feet.
SNIP
'But the Orcs have brought a devilry from Orthanc,' said Aragorn. 'They have a blasting fire, and with it they took the Wall. If they cannot come in the caves, they may seal up those that are inside. But now we must turn all our thoughts to our own defence.'
~Ch. 7 Helm's Deep