Ark of the Covenant - Bible History Online
Bible History

Naves Topical Bible Dictionary

MORTAR, 2. A cement

=>To be trodden to make firm

Nahum 3:14

14. Draw thee waters for the siege, fortify thy strong holds: go into clay, and tread the morter, make strong the brickkiln.

To be trodden to make firm - MORTAR-2. A cement MORTAR in Naves Topical Bible (Bible History Online)