Rothschilds started out as a small time lender and merchant of medals and rare coins. By 18 25, they had gotiated loans for britain, prussia, austria, russia and france. They could offer to help issue the bonds for much lower fees than any one else. This creates incredible arbitrage opportunities. If you know where gold is being sold for a hundred dollars and it's being sold for 90 dollars - that doesn't seem like a big difference in paris or vienna. But if you can just tell amshell in vienna to buy up some british government bonds really quick...they can turn a real profit.