The first aqueduct was built by Herod (37BC to 4BC), at the time the new city was founded and dedicated to the Roman Caesar, Augustus. It brought the water from the southern side of Mount Carmel, at Shummi, about 10KM to the north east of the city. The water flowed on a single raised canal, and in one section it is dug into the rock (at Jiser e-Zarka, an Arab village north of Caesarea).
Since even this was not sufficient, a second aqueduct was built by the Legions of the Emperor Hadrian (2nd C AD). It brought water from Tanninim (Crocodiles) river, farther from Shummi. This section, with a tunnel of about 6KM long, was tapped into the older aqueduct, and doubled its capacity. This new source of water was added to the right of the first canal, and the aqueduct was thus doubled in width. The builders used the same building materials and style, so it is hard to see that the pair of tunnels were built in different ages.
These twin parallel aqueducts, termed today as the High-level aqueducts, continued to supply water for 1200 years. During the ages it was repaired several times. In the marsh lands east of Jiser e-Zarka a bypass canal was built to overcome the damages.
After that time the aqueduct was beyond repair. Therefore, in the Crusaders period (12th Century A.D.), a third, smaller, canal was built that replaced the first two. At that time the City was smaller and required less water, so the third smaller canal was sufficient.
Another (forth) lower aqueduct was built during the Byzantine period in order to satisfy the growing needs for fresh water supply to the large city. This aqueduct started from a new source of water: the springs at Maagan Michael, several kilometers north to Jiser-E-Zarka. Since the water level was too low, a dam was built in order to create a lake, thus raising the water levels at the source. Then, a canal was dug in the sandstone ridge and brought the water to the city. This canal was laid lower and to the east of the raised Aqueduct.
Caesarea, 2014, Israel.