Love coins that tell story. The condition of them, where they are found, how people used them at the time, details about the society.

Would never have never thought of Arab-Viking trade.

What's interesting is that basically all the best preserved coins from the start of the Arab conquests into the late 11th century are found in Viking hordes in Scandinavia and Russia. The Vikings traded furs with the Arabs, and there were massive trade routes that would follow the Volga river down into present-day Iran and Turkey. And because Muslim coins didn't use iconography at all, they're amazing resources for history. They have dates, rulers who minted them, mint site, etc. Really fascinating subject.