Joshua 6:19

“ But all the silver and gold, and vessels of brass and iron, are holy to YHWH. They shall come into the treasury of YHWH.”

These things were mentioned as the most valuable and desirable, but, as the people were aware, everything in the city was devoted and belonged to YHWH exclusively. Nothing must be retained for personal use. Their idols should be destroyed in fire (Deuteronomy 7:25). Anything of value would go into the treasury in the Tabernacle for religious use (compare Numbers 31:54), probably after passing through fire or water (Numbers 31:22). This would contribute to the lack of archaeological artefacts as all would be gathered up that much more carefully because they were YHWH's. At this time the vessels of iron would have been imported and valuable.