וַיִּֽטַּהֲר֔וּ הַכֹּהֲנִ֖ים וְהַלְוִיִּ֑ם וַֽיְטַהֲרוּ֙ אֶת־הָעָ֔ם וְאֶת־הַשְּׁעָרִ֖ים וְאֶֽת־הַחוֹמָֽה׃
And the priests and the Levites purified themselves; and they purified the people, and the gates, and the wall.
Read midrashic interpretation of Nehemiah 12:30: and classical rabbinic exegesis.