On that day opens a new subparagraph covering verses 11-14.
The mourning in Jerusalem will be as great refers to the sorrow over the one pierced, as described in verse 10. In some languages mourning in this clause needs to be translated with a verbal expression; for example, “the people of Jerusalem will mourn as much as…” or “… will cry as bitterly as….”
As the mourning for Hadad-rimmon in the plain of Megiddo: This clause constitutes a third comparison, again emphasizing the intensity of the mourning. The point of the comparison, however, is not entirely clear. The Hebrew is literally “as the mourning of Hadadrimmon…” (King James Version, Revised Version). As so often where a phrase including “of” is concerned, the relationship between the nouns it links is ambiguous. The traditional interpretation takes Hadad-rimmon as a place name, though it is a name that occurs nowhere else. Jerome identified it with a village near Jezreel in the plain of Megiddo. If this is correct, the mourning is probably related to the death in battle of Josiah, the last good king of Judah, in 609 B.C. at Megiddo (2 Kgs 23.28-30). From the longer account in 2 Chr 35.20-27, we know that there was some sort of regular commemorative mourning for Josiah even after the exile. Thus this verse could be referring to a practice still current in the writer’s own day. Translators who regard Hadad-rimmon as a place name should make it clear by translating “mourning at Hadad-rimmon” (New Jewish Publication Society’s Tanakh, Beck).
In more recent times, scholars have suggested that Hadad-rimmon is the name of a Canaanite god, a composite name incorporating the Syrian (“Hadad”) and Assyrian (“Rimmon”) names of a god of storm and rain (compare the Good News Translation footnote). There is some evidence of ritual mourning for such a god in connection with the annual cycle of vegetation, and there may be references to this practice in Jer 6.26; Amos 8.10 (compare Ezek 8.14). Most modern translations seem to prefer this view. Translators who regard Hadad-rimmon as the name of a god should make it clear by translating mourning for Hadad-rimmon (Revised Standard Version/New Revised Standard Version, Good News Translation, New Jerusalem Bible) or “mourning over Hadad-rimmon” (New English Bible/ Revised English Bible).
Neither view can be proved or disproved, but in the context a reference back to the tragic death of Josiah seems more likely than a reference to a pagan ritual, and we would tentatively recommend that translators take Hadad-rimmon as a place name.
The plain of Megiddo is a fertile agricultural area in the north of Israel, also known as the valley of Jezreel (Jdg 6.33; Hos 1.5) and as the plain of Esdraelon (Judith 1.8; 3.9; 4.6; 7.3). Megiddo is a town at the southwestern edge of the plain. A plain is a flat area and may be translated here as “flat lands [or, flat place] near Megiddo.”
Quoted with permission from Clark, David J. & Hatton, Howard A. A Handbook on Zechariah. (UBS Helps for Translators). New York: UBS, 2002. For this and other handbooks for translators see here .