For nearly 19 centuries, water has played a central role in Istanbul's growth, with a vast network of reservoirs, aqueducts, galleries, distribution points and fountains evolving from the Roman and Byzantine eras through the Ottoman period to the present day.

The historic system reached its peak during the Ottoman period with the Kırkçeşme Water System built by Mimar Sinan, an approximately 55-kilometer (35-mile) engineering network stretching from Belgrad Forest to the heart of Istanbul.

Today, thousands of people pass beneath the Bozdoğan Aqueduct, visit Belgrad Forest, gather at Taksim Square or walk past the water gauge on the wall of Şehzade Mosque without realizing that these landmarks are connected to the same centuries-old water infrastructure.

The surviving reservoirs, aqueducts, galleries, distribution points and fountains represent an "invisible water civilization" that helped make Istanbul's expansion possible.

Water system dates to Roman era

Istanbul's documented water history dates back approximately 19 centuries. The city's first known water facilities were built during the reign of Roman Emperor Hadrian between A.D. 117 and 138.

As the population grew, water from sources outside the city was transported through canals and waterways. By the fourth century, increasing demand led to the development of additional transmission lines, including the system associated with the Valens Aqueduct, known today as the Bozdoğan Aqueduct.

After the Ottoman conquest, Sultan Mehmed II repaired deteriorated Roman and Byzantine waterways and restored them to operation. Later Ottoman sultans continued expanding the infrastructure.

During the reign of Sultan Suleiman the Magnificent, architect Mimar Sinan built the Kırkçeşme Water System, giving Istanbul one of the most advanced water infrastructures of its era.

The system included 33 aqueducts, kilometers of galleries, inspection shafts, water gauges and distribution structures. It became one of the largest engineering projects of the 16th century.

The historic water journey began in Belgrad Forest, where the Valide, Topuzlu, Kirazlı and Sultan Mahmud reservoirs collected rainwater and spring water that supplied the system.

Water traveled along two main eastern and western branches before converging at Başhavuz, a reservoir approximately 14 meters deep south of Kemerburgaz.

Described by Mimar Sinan as being "as deep as the Galata Tower," Başhavuz, which means the main pool, was a critical point where water from different sources was collected and allowed to settle before entering the main transmission line.

From there, water passed through the Mağlova Aqueduct and continued toward Istanbul through the Uzunkemer, Güzelcekemer and Paşakemeri aqueducts.

The Mağlova Aqueduct, approximately 36 meters (118 feet) high and 250 meters long, features a two-tiered supporting structure. Its architecture and engineering have made it one of the most significant examples of Ottoman and global water engineering.

Water eventually reached the city through the Bozdoğan Aqueduct. Completed in A.D. 378 during the reign of Emperor Valens, the aqueduct was repaired repeatedly during the Ottoman period and continued to serve Istanbul's water system.

Taksim's namesake water system

Water's journey through the city continued through distribution points, including Taksim.

Water arriving in the city was divided and directed toward fountains and other distribution points. This process of "taksim," meaning division or distribution, eventually gave the surrounding area its name.

Another major distribution point was Eğrikapı Maksemi. The octagonal distribution point associated with Taksim was completed during the reign of Sultan Mahmud I and divided water among neighborhoods and fountains.

Following the construction of the Kırkçeşme system, more than 30 fountains were supplied with water, a significant capacity for the 16th century.

Kadir Pektaş of Istanbul Medeniyet University's Department of Art History said water had been decisive in the establishment and growth of major cities throughout history.

He said Istanbul's water infrastructure originated in the Roman period and was subsequently developed by Byzantine and Ottoman rulers.

Pektaş noted that water was later brought to Istanbul through Istranca and Çatalca during the reign of Constantine the Great, while the use of Belgrad Forest as a water source also dates to the fourth century.

He said the Ottoman Empire preserved and expanded the existing infrastructure after conquering Istanbul, with Sultan Mehmed II repairing waterways and aqueducts and subsequent rulers adding new facilities.

Pektaş said the Kırkçeşme system was constructed on Sultan Suleiman's orders after the sultan noticed water sources around Kağıthane and Belgrad Forest during a hunt.

According to an account attributed to Evliya Çelebi, Mimar Sinan warned that the project would cost as much as sacks of coins laid end to end from Belgrad Forest to Istanbul. Suleiman reportedly replied that the sacks could be placed "side by side" if necessary, as long as Sinan brought the water to the city.

The system initially supplied approximately 17,500 cubic meters of water to Istanbul per day. With later additions, its capacity increased to as much as 30,000 cubic meters.

The system relied on underground pipes, water gauges and distribution points as well as aqueducts.

Pektaş said water gauges, including those still visible on the outer wall of Şehzade Mosque, regulated pressure and prevented high water flow from damaging pipes.

They also raised water to higher levels and allowed it to come into contact with air, contributing to the preservation of water quality.

Inspection shafts were placed along the galleries at intervals of 20 to 40 meters, while newly discovered water sources could be incorporated into the network.

Pektaş described the Mağlova Aqueduct as one of the clearest examples of Mimar Sinan's engineering abilities, comparing its importance in water architecture to the Selimiye Mosque's importance in centrally planned mosque architecture.

Istanbul's 'invisible backbone'

Pektaş described the historic waterways as Istanbul's "invisible backbone," saying millions of people pass these structures every day without realizing they form part of one interconnected system.

He recommended installing information panels explaining the history and function of water gauges, distribution points and other structures, particularly because some are mistaken for tombs or other buildings.

He also proposed creating a cultural tourism route stretching from Belgrad Forest to Kağıthane Valley, connecting reservoirs, aqueducts, galleries and other water structures.

Such a route, he said, would allow visitors to understand the system as a whole and follow the development of Istanbul through its waterways.

Pektaş said the Ottoman water system was more than an engineering project, as water occupied a central role in urban and social life and reflected the empire's approach to urban planning and civilization.

He also called for the restoration of the fountains that gave the Kırkçeşme Water Facilities their name.

The fountains, located near the Bozdoğan Aqueduct, were dismantled in the 1940s during the construction of Atatürk Boulevard. Their stones were numbered with plans for reconstruction, but the project was never completed.

Pektaş said the fountains should be restored either according to their original function or at least symbolically, helping preserve the memory of the centuries-old water system.