The cistern of the Holy Apostles was begun in 1825 and completed in 1846, the date cut into the paving of its catchment surface. The decorative pillars were added in 1848, and the approach was finished in 1851, according to the Book of the Elders of Paxos.
It is without question the most elaborate cistern on the island and one of the best pieces of British public building in the region. It has been a protected monument of the Ministry of Culture since 1982.
Unlike the cylindrical cistern of the Holy Anargyroi on the east side, this one is rectangular, with a monumental central staircase on its south face. The rectangle holds not only the main tank but also a long settling tank along the north side, about a third of the size of the main one. Three openings in the dividing wall let the water pass from the settling tank into the main tank once the silt has dropped out.
The cistern collects water not only from its paved catchment but from the unenclosed ground around it, which is why the shaping of the whole surface mattered as much as the tank itself.
Getting there: almost in the middle of Gaios.
The main tank is vaulted and about six and a half metres high; its outer walls are built like a retaining wall, wider at the base to carry the water pressure. Two elegant round orifices sit symmetrically on its centreline. The three square openings on the north side are for cleaning, and the intake spouts behind them are now filled with nine circular glass blocks.
Small settling basins stand in front of the two intake spouts along the duct on the north side. The cistern was repaired in 1931 and again in 1999. The overflow of the Mantropoulos cistern, out on the edge of the settlement, is still piped into this one today, though since the open reservoirs were built it is no longer the main water supply of Gaios.
The monumental stairway is out of all proportion to the job: it would suit a palace or a country mansion rather than a rainwater cistern.
Its capacity is seven hundred and twenty cubic metres, by far the largest on the island.
