דָּרַ֥כְתָּ בַיָּ֖ם סוּסֶ֑יךָ חֹ֖מֶר מַ֥יִם רַבִּֽים׃
Thou hast trodden the sea with Thy horses, the foaming of mighty waters.
Rashi on Habakkuk
You trampled in the sea You trampled upon [Sennacherib’s] hordes, which were as heavy as the sand by the sea.
Rashi on Habakkuk
a heap of many waters Jonathan renders. upon a heap, an expression of (Exod. 8: 10) “many heaps.”