Joan Kennedy Biddle, a 77-year-old Tampa resident, is suing to collect on a $300 loan her great-grandfather made to the city during the Civil War. Of course, she also expects to be paid interest on the loan, and at 8%, the debt has grown to just shy of $23 million.

Biddle has a 147-year-old IOU that was signed by Tampa’s then-mayor. It promises to repay Biddle’s ancestor for the borrowed money used to purchase supplies to defend the city.

Tampa has come up with a laundry list of reasons why the debt isn’t valid. Topping it all off is that the money is payable in Confederate dollars — not exactly common (or usable) these days.