Pigeon tower, a source of fertilizer

Pigeon tower was used as a safe house and shelter for the pigeons but this wasn’t the only function. They were built around the farms to collect their droppings as fertilizer! Every 6 month the farmers collected the dropping and used them in their farms or even they sold it. Today we know that these droppings are rich in Nitrogen, a critical element for cucurbits such as melons. No surprise that melons of Isfahan have had a reputation since 1000 years ago.
The structure includes a central cylinder which is surrounded by several smaller cylinders; all are made of brick and plaster. There are thousands of nests on the internal surface of the cylinders.
The only entrance to the tower was a set of holes on the top, just as big as a pigeon, to prevent the birds of prey from entering the tower. There is also a white stripe around the external surface of the tower which is slippery for snakes.
Pigeon towers are only found in Isfahan province and some of these organic fertilizer factories are reconstructed for the people and tourists to visit.