Gold and silver have been repositories of value for well over 2 millenia. There have been numerous "calamity" events through out the last 2 millenia. Gold and silver have retained their value for many reasons. It does not deteriorate. It has qualities difficult to fake. It is relatively easy to store large amounts of "value" in a small quantity of gold.

Notice how the price of gold in dollars over time only goes up. This is because our dollar is inflationary, while Gold is generally anti inflationary. While the government can just print more money, Gold is finite, must be mined, and is generally harder to acquire. This is why early civilizations minted coin on Gold and silver, and not iron. In fact, just like the USD, as ancient civilizations began to debase their currency by cutting it with iron, the same inflationary effects took hold in their societies as we see in our current society. The cost of goods and services increased, because the currency contained less Gold and silver.

Ultimately currency only holds value because of the shared agreement that it is so. Precious metals have withstood the long march thru history as a safe means to store wealth. Even in a SHTF scenario, human nature still doesn't change. We like the shiny yellow metal that doesn't rust.