Among other structures, this involved the spectacular Pontcysyllte Aqueduct over the River Dee in the Vale of Llangollen, where Telford used a new method of construction consisting of troughs made from cast iron plates and fixed in masonry. Extending for over with an altitude of above the valley floor, the Pontcysyllte Aqueduct consists of nineteen arches, each with a span. Being a pioneer in the use of cast-iron for large scaled structures, Telford had to invent new techniques, such as using boiling sugar and lead as a sealant on the iron connections.