Of the over 150 cisterns located within the city walls of Istanbul, the Nakilbent cistern is a beautifully preserved example of a 6th century Byzantine cistern. Built during the reign of Emperor Justinian (527-565 AD), the cistern’s interior reveals 18 marble columns supporting brick arches. Seven of the original marble columns have been reinforced during the Ottoman period, and are now surrounded by brick and stone piers. This cistern would have been used as a private water source for the large palace within which it was located. Most likely, this was not originally part of the Great Palace of Constantinople. However, the Nakilbent cistern is located in an area that would have fallen under the expanded palace grounds, when, at the end of the 7th century, Justinian II built 2 large halls, the Lausiakos and the Triklinos. These were later incorporated more completely into the palace grounds under Theophilus in the 9th century.