וְהָי֥וּ שָׁמֶ֛יךָ אֲשֶׁ֥ר עַל־רֹאשְׁךָ֖ נְחֹ֑שֶׁת וְהָאָ֥רֶץ אֲשֶׁר־תַּחְתֶּ֖יךָ בַּרְזֶֽל׃
And thy heaven that is over thy head shall be brass, and the earth that is under thee shall be iron.
Read kabbalistic (mystical) interpretation of Deuteronomy 28:23: and classical mystical sources.