This is the big rainwater cistern of Es Mercadal. You will find explanations in the photo of the poster later in the series. What the poster doesn't say, is that the word <i>aljub</i>—<i>aljibe,</i> in Castilian—comes from the Arab <i>al-ğubb,</i> cistern, specifically a cistern built under a house to store rainwater collected on the roof.(1) There are many variations. Not all these cisterns are under houses. In the countryside, for example, they were built above ground, like this one in Mercadal, or carved into the rocks. And like this one, they collect the rainwater that falls on a large, open, and inclined platform, into the well below. See the next photos in the series. In the countryside, the cisterns have on the roof a system of pulley, rope, and bucket.<br>
(1) The Arabs came to the island sporadically between the 7th and 10th centuries. These incursions were nothing more than pillaging raids. In the 10th century, however, the Balearic Islands were formally annexed to the caliphate of Cordóba. It is only in 1229 that Jaime I of Aragón took possession of the archipelago. So, all in all, the Arab presence in Menorca lasted about six centuries. Its influence is felt to this day.
<a href="//commons.wikimedia.org/wiki/User:Nicolas_G._Mertens" title="User:Nicolas G. Mertens">Nicolas G. Mertens</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>