Water management in ancient Alexandria , Egypt . Comparison with Constantinople hydraulic system

The collection, evaluation and listing of all available data related to the supply, collection and disposal of water is a project of combining and recording all the data for infrastructure projects and their structure within the urban structure of Alexandria and the wider region, as it was discovered and studied to this day. The paper is a description of the most important storage structures for the waters of the Nile River and the rain. Composing data from previous descriptions, archaeological excavations and random discoveries during construction work created a database. This database currently has 144 tanks of 1 to 4 levels, from 6 m to 2,500 m. In particular, they have identified 27 tanks on 1 level, 50 tanks on 2 levels, 49 tanks on 3 levels, 9 tanks on 4 levels and 9 tanks whose exact morphology is unknown to us. The examples of reservoir technologies and management practices given in this work may be of some importance to the sustainability of water resources for the present and the future. Reservoirs have been used to store both rainwater and spring and river water to meet the needs of seasonal variations. The tanks range from simple to large underground structures. Then, a comparison is made with the water management systems in the wider Mediterranean region and especially in Istanbul, where there is such infrastructure.


INTRODUCTION
The need for water as a vital element of human existence led the ancient world to incessant care for its better management. The provision of adequate and clean water and the operation of a complete sanitation network are undoubtedly the most essential applications of hydraulic technology and the basic infrastructure of the most organized cities. The provision of ancient civilizations to ensure adequate amounts of water for daily activities and to ensure the collection or removal of rainwater and dirty water are observed by almost all excavating missions and are reflected in written sources (Angelakis & Spyridakis ).
Unlike the preceding civilization of Egypt, which was based on the exploitation of the abundant waters of the large Nile river, the city of Alexandria has been plagued by limited, often scarce and inadequate natural water resources (Butzer ).
The adoption of the design of Hippodamus during the Hellenistic era created residential renewal in the cities under construction, and it was, from the outset, fertile ground for the implementation of the most innovative hydraulic infrastructure of their time (Bacon ).
Since the founding of Alexandria, a coastal city in ancient Egypt, the use of facilities and infrastructure for groundwater exploitation and wastewater management has been studied and designed, and over time, as the city grew, management expanded their development and adaptation (Hairy ). The calculation of groundwater required an accurate knowledge of both the stony nature of the geological formations and their location, layout and 'architecture'.
The determination of hydrogeological structures allowed the Alexandrian engineers to determine the shape and dimensions of the aquifers. Their exploitation required complex techniques, as they were renewable water sources. The volume of exploitable water also had to be assessed in order to adapt the structures for water supply and wastewater accordingly (Hairy a, b).
Despite its location on the Egyptian coast, bathed in the waters of the Mediterranean and Lake Mareotidos, the city of Alexandria has always had a shortage of drinking water ( Figure 1). The place that Alexander the Great chose for the founding of his city was a barren area, where there were only brackish wells. Various intelligent systems were implemented from the first days of the city's founding: the supply of water from the Nile through the opening of a canal (Schedia, Centia), its distribution with a branched pipeline system and the storage of water in many underground tanks (Hairy ).
The ancient city of Alexandria, which has evolved into the most cosmopolitan and vibrant metropolis of the Mediterranean, is often referred to as the city of reservoirs (Empereur ).
The whole city was basically built on a level of sewerage and water supply infrastructure, which ran underground from the south to the north and ended at the sea. According to written sources, Ancient Alexandria was built over a network of water canals that operated under the city streets.
The roads intersected in order to take advantage of the air currents coming from the sea to cool the city in a natural way, to keep the inhabitants healthy, and to give the city a bioclimatic character (Empereur ).
In recent decades, successive archaeological excavations in and around the city have uncovered, in the ruins of various buildings, public baths and pipes, sewer sections, ceramics and occasional indications for the use of covered sewer systems for rainwater and sewage. In addition, part of the internal sewer system of some modern homes was found to be directly connected to the Although several studies have traced and presented traces of water supply and water distribution systems in ancient Alexandria, there is still a lack of sufficient data on waste management and sewerage. This lack allows us to present an overview, rather than a fragmentary picture, of the complete and innovative management system mentioned in the historical sources (Ferro & Magli ).
However, the indisputable fact is that most travelers and historians of ancient times describe, impressed, the number, size, complex operation (collection of river and rainwater) and the majestic construction of water storage tanks that existed in the city (Fraser ).
This study aims to highlight the infrastructure of ancient Alexandria, identifying the structure of sewerage systems and highlighting the importance of sewerage and water management systems as the basic principles on which the hygiene of the city's inhabitants depends.
So wisdom in management seems to be the solution to the ever-growing global water resources problem rather than engineering development, as was previously suggested (Angelakis et al. ).

Topography and urban planning of Alexandria
The architect Deinocrates of Rhodes designed Alexandria, in the form of a rectangle (grid). It was an important city of the ancient world ( Figure 2). For more than two thousand years, it was the largest city in Egypt and was its capital for almost half of this period. As an important trading position between Europe and Asia, it has benefited from the easy land connection between the Mediterranean and the Red Sea. On July 21, 365 AD, a tsunami caused by an earthquake centered in Crete struck Alexandria. Many historians and scholars estimate that the event contributed to the gradual decline of the state city, because in addition to the millions of victims among the population, much of its coastline sank in Mediterranean waters in addition to water in drinking water supply canals water becoming brackish (Decobert ; Hairy a, b).
After the tsunami of 365 AD, the Alexandrians depended exclusively on the reservoirs, as the groundwater became salty. There were smaller private and medium-sized or larger public tanks that served the city, as well as tanks intended for mosques and madrassas (Islamic seminaries) during the Islamic period. The construction of reservoirs was vital in Alexandria and so an advanced architecture was developed for them, with differences proportional to the different historical periods (Greek, Roman and Islamic) (Decobert ). These large underground reservoirs were developed in height on many levels with columns and dividing arches. Remains of the infrastructure of the byzantine period were used as building materials.

The tanks (cisterns) of Alexandria and their construction features
Drinking water was a valuable commodity in this barren area without natural sources of fresh water. The need for storage led to the construction of buildings in the form of large, closed, watertight, compact tanks that maintained the freshness of the water. The first tanks in Alexandria date back to the Ptolemaic period. They are fed artificially or by collecting rainwater. They are located in places where access to water is difficult, in special facilities such as thermal baths or necropolises, or even in areas with craft activities.
Their shape varies depending on the time they were made. Thus, during the Ptolemaic period, the tanks were small, just dug into the rock and often adopted the socalled 'bottle' as a shape. The techniques were perfected in Roman times. At this time, the tanks are made of bricks connected with plaster and are watertight, covered with ceramic mortar (from fragments of tiles and bricks). They are small and adopt as a shape the so-called 'tree'; that is, a set of decreasing volumes, which are connected to each other by vaulted passages. They gradually become larger and adopt a form known as 'welded volumes'. At the end of antiquity, they had a roof and were powered by an aqueduct (Ahmed et al. ).
Overuse and artificial feeding of most tanks, however, led to network damage that affected water quality. In addition, the year 365 AD tsunami caused large amounts of salt water to invade the earth, destroying the city's aquifer. The gradual sinking of part of the coast also put the freshwater network in contact with seawater (Angelakis

).
This is why the system was completely redesigned in the 5th century AD. New public tanks were created, larger in size, and a freer design was adopted. These reservoirs were filled with fresh water during the Nile flood season.
During the Arab conquest, this system of reservoirs was abandoned and reused only when Ahmed Ibn Toulon (835-884 AD) adopted the construction of multi-storey tanks that were fed either by the flood of the Nile River or from rainwater collection. They brought a sakieh pumping system and a compluvium (rainwater collection system), of which remains have been found on the roofs of many of them (Empereur ). Some were connected to each other by a network of underground pipelines (Hairy ).
The dimensions of the tanks are extremely variable and depend directly on their destination, from a few cubic meters for a private home to a medium and large capacity with several thousand liters for a public building such as the baths of Kom el-Dikka (Greco-Roman time). The bulky tanks were intended for public use. Mediums may have been suitable for feeding a neighborhood or a group of dwellings (Butzer ).
A characteristic type of architecture distinguished it.
Their volumetric capacity could reach 2,500 m 3 . The excavations showed that they used special plaster in the masonry and the floor. The tanks were usually underground and covered with a roof to prevent external contamination.
These public structures were on one, two, three, or even four levels. The pumping holes were placed in the roof.
Their maintenance was carried out due to a drainage well, which provided access to the bottom of the tank, the depth of which could reach 13 m. With a semicircular shape, this well was usually placed around the perimeter of the building and often at one of the corners. The descent takes place through a staircase located on the walls of the well. This option allowed the tank to be cleaned before the annual filling, which was necessary to ensure good water quality (Guyard ).
The internal support system of this type of tank is based on a structural element with a square shape, whose average and (e) 9 tanks whose exact morphology is unknown to us.
Examining the morphological data recorded, five more general types of tanks can be identified (Table 1). The issue of their dating remains unresolved.
Other reports mention that 500 tanks are known from the more than two thousand that existed. Sedimentation  Another tank is the one that was discovered during the restoration and renovation work (Figure 7)

Rainwater management
Especially in the city of Alexandria, the composition of all the data proves that there has always been care for the utilization of rainwater.    One of the most characteristic cases was the Complex of Serapio (Figures 9-11). There contained, among other structures, the Nilometer system, which also functioned as a rainwater collection tank (Rowe ).
In parts of the roof of some tanks in the Arab city, such as the El Gharaba and El Nabih reservoirs, grooves have been discovered connected to openings that ended inside the reservoir. A second addition is installed in the form of a pipe, at an incline that also ends at the tank (Guyard ; Hairy a, b).
We can therefore conclude that in the effort to utilize all available water during the period of the year when the quantities transported by the network of canals were small, the network also had infrastructure for the collection and storage of rainwater (Shafy et al. ).

DISCUSSION AND CONCLUSION
In the light of new discoveries and combined studies, however, the belief is beginning to form that Alexandria can be compared to Constantinople, which until now has been called 'the city of tanks'. The number of 144 large tanks revealed so far is greater than the approximately 100 surviving in Istanbul. Although not comparable in size it is just as majestic. The largest tank discovered in Alexandria, El Nabih has a storage capacity of 2,500 m 3 . Continuation of the investigations will probably reveal the quantities of water stored for it compared to the approximately 1,000,000 m 3 that could be collected in total in the cisterns of Istanbul (Ciniç ; Bogdanović ).
Another question that can be asked is that of their archi-    The evolution of rainwater collection systems to increase water use efficiency and the ongoing effort to preserve the environment for sustainable development has been presented and discussed in this paper. It is believed that these early sys- (c) Ancient reservoir water technologies should not be considered as historical objects, but as possible models for sustainable water technologies for the present and the future.
(d) Ancient water technologies, such as tanks, were characterized by simplicity, ease of operation and the requirement for complex controls, making them more sustainable (Mays ). However, the successful design and operation of some of them systems were huge achievements in engineering.
(e) Reservoirs have been used by ancient civilizations for the sustainability of water resources and have been used since, although their importance for today's water supply purposes has somewhat disappeared in developed parts of the world, despite the fact that it has continued in many developing parts of the world (Mays ).

DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.