וְהִקְרִיתֶ֤ם לָכֶם֙ עָרִ֔ים עָרֵ֥י מִקְלָ֖ט תִּהְיֶ֣ינָה לָכֶ֑ם וְנָ֥ס שָׁ֙מָּה֙ רֹצֵ֔חַ מַכֵּה־נֶ֖פֶשׁ בִּשְׁגָגָֽה׃
then ye shall appoint you cities to be cities of refuge for you, that the manslayer that killeth any person through error may flee thither.
Read kabbalistic (mystical) interpretation of Numbers 35:11: and classical mystical sources.