When was the first iron arch bridge constructed?

In 1811 Palmer built the first American covered bridge over the Schuylkill River in Philadelphia. This was a continuous three-span arch truss consisting of two 150-foot spans and one 195-foot span. It is recorded that the city bridge committee in­sisted that the heavy timbers be covered with a roof and siding to preserve and protect the structure from weathering. The bridge thus became known as the Permanent Bridge