בַּיּ֣וֹם הַה֗וּא יִגְדַּ֤ל הַמִּסְפֵּד֙ בִּיר֣וּשָׁלִַ֔ם כְּמִסְפַּ֥ד הֲדַדְ־רִמּ֖וֹן בְּבִקְעַ֥ת מְגִדּֽוֹן׃
In that day shall there be a great mourning in Jerusalem, As the mourning of Hadadrimmon in the valley of Megiddon.
Read midrashic interpretation of Zechariah 12:11: and classical rabbinic exegesis.