Medieval Alhambra’s Pulser Pump And Other Aquatic Marvels

Recently the Practical Engineering YouTube channel featured a functional recreation of a pump design that is presumed by some to have been used to pump water up to the medieval Alhambra palace and its fortress, located in what is today Spain. This so-called pulser pump design is notable for not featuring any moving parts, but the water pump was just one of many fascinating engineering achievements that made the Alhambra a truly unique place before the ravages of time had their way with it.

Although the engineering works were said to still have been functional in the 18th century, this pumping system and many other elements that existed at the peak of its existence had already vanished by the 19th century for a number of reasons. During this century a Spanish engineering professor, Cáceres, tried to reconstruct the mechanism as best as he could based on the left-over descriptions, but sadly we’ll likely never know for certain that it is what existed there.

Similarly, the speculated time-based fountain in the Court of the Lions and other elements are now forever lost to time, but we have plenty of theories on how all of this worked in a pre-industrial era.

Evening panorama of Alhambra from Mirador de San Nicolás, Granada, Spain. (Credit: Slaunger, Wikimedia)

A UNESCO World Heritage Site since 1984, the Alhambra saw its first construction in 1238 CE by Muhammad I, the first Nasrid emir. The Nasrid dynasty would last from 1238 to 1491 CE when the Muslim state of al-Andalus fell during the Christian Reconquista.

Even after the end of the Nasrid dynasty would the Alhambra see further construction by Charles V in the 16th century. This made the Alhambra a rather unique amalgamation of Islamic and Renaissance-era architecture and engineering. Sadly by the 18th century the structure had been abandoned for centuries, invaded by squatters, and partially destroyed by the troops of Napoleon in 1812.

Only after these troubled times did an appreciation for such cultural heritage begin to flourish, with European and American tourists alike frequenting the area. One of them – US author Washington Irving – was so inspired by his visit in 1828 that he’d end up writing Tales of the Alhambra, containing many myths, stories, sketches, and essays pertaining to the site. This book in particular was instrumental in making an international audience aware of this site and its legacy.

This renewed attention resulted in the site becoming recognized first as a Spanish Cultural Heritage monument in 1870 and subsequently by UNESCO more than a century later.

Water Features

Most fortresses of the era relied primarily on water cisterns that collected rainwater, as well as access to local rivers in some form, usually requiring human or animal labor to transport the latter. This was also how the Alhambra started in its initial fortress form, called the Alcazaba, meaning ‘citadel’ in Spanish, from Arabic al-qaṣabah. The water from this cistern didn’t just supply drinking water, but also for the bathhouse (hammam) and water elements like a pool or fountain for houses in the interior urban area. These houses additionally featured latrines that were flushed using this cistern water.

As the Alhambra expanded, with many palaces and related structures added, its water requirements increased correspondingly. Rather than some small decorative water features for a dozen houses and a communal bath, there were now reflective pools, fountains and a much larger population. This necessitated finding more efficient ways to get more water up the hill on which the Alhambra was constructed.

Aqueduct of the Alhambra as it enters the wall. (Credit: Sharon Mollerus, Wikimedia)

In addition to the aforementioned pump, there was also an aqueduct (the Acequia Real) that carried water from the Darro River. At a distance of 6.1 km from the fortress the river is at a sufficiently high elevation to provide water using just gravity. This aqueduct additionally provided water via additional branches to gardens and settlements beyond the Alhambra’s walls.

Many details can be found in this 2019 summary of applied hydraulic techniques at al-Andalus fortresses by Luis José García-Pulido and Sara Peñalver Martín.

As noted in that overview article, the reason for the Alhambra being significantly more advanced than other fortresses in the al-Andalus region was that it was the seat of the Nasrid dynasty, ergo it was only natural that it’d not only get all the palaces and comforts, but also the most advanced technologies for supplying water.

Unfortunately the unique pumping device that was used to supply the Alcazaba with water from the aqueduct was replaced in the 18th century with a more basic syphon system and the original device was removed. Up till that point the previous device had continued to work, despite the new owners of the Alhambra not understanding its operating principles. This left 19th century researchers like Cáceres to essentially fully rely on notes made during the previous century.

That said, there are also hints that the Alcazaba of the Antequera fortress used a similar device to pump water uphill, featuring ceramic pipes and other features that are described in by Sancho de Toledo in 1545. Unfortunately these accounts were all written by people who lacked the engineering know-how of the original Nasrid engineers – or any engineering knowledge at all – and thus had no understanding of the workings of these pumps.

This means that we will unfortunately never know exactly what this device looked like or how it worked, but we can still look at some mechanisms which we are familiar with today that could have been used. The concept of the hydraulic ram or pulser pump would seem to come closest compared to what little we do know.

Self-Powered Pumps

1. Inlet – drive pipe; 2) Free flow at waste valve; 3) Outlet – delivery pipe; 4) Waste valve; 5) Delivery check valve; 6) Pressure vessel (Source: Wikimedia)

Unlike a water pump that uses e.g. an impeller to impart kinetic energy and thus move the liquid, a self-powered pump uses physical phenomena like the water hammer effect or the fact that gas in a liquid will rise in order to effect a pumping effect. The hydraulic ram, for example, uses the water hammer effect and relies only on the kinetic energy of the incoming water.

The basic hydraulic ram functional sequence involves the water current pushing the normally open waste valve close, at which point the water hammer effect from the sudden current cessation forces the delivery valve open and pushing water into the delivery pipe.

This process will reverse again after a short while,  sending a pressure wave upstream and eventually leading to the waste valve reopening. The downstream flow will then resume again, restarting the whole process.

In terms of technological complexity this is a very straightforward design, with the most complex parts being the valves and the pressure vessel that cushions the system against pressure shocks. This is however a design that would have been technologically quite feasible to manufacture and operate.

Basic pulser pump design. (Credit: Belbury, Wikimedia)

Another, similar type of pump is the gas lift pump. A very small variant of this is commonly used in devices like coffee percolators, with the pulser pump being in effect a very large implementation of the same general principle. Rather than applying heat to the water reservoir in order to create gas (i.e. steam), the pulser pump uses an air compressing effect that’s also used with water-powered trompe air compressors.

As water falls down a pipe it drags air bubbles along with it, which eventually arrive at the bottom where said air is trapped in a cavity while the water flows on to a lower elevation.

The thinner pipe through which water ultimately is pumped is inserted into this air chamber in such a way that it’ll alternately ingest water and air as the level of the latter varies over time. This way pockets of water become trapped between pockets of air, with a resulting pulsing output of water at the end of this pipe.

Whether the original device at the Alhambra or Antequera exactly matches either pump design will likely remain forever a mystery, but neither were beyond the technological means of the time, with the pulser pump arguably even more straightforward due to a lack of need for any valves and pressure vessels.

Time Or Reflective Fountain

Although the Practical Engineering video focuses on this pump design, its author – Grady – was inspired by a Primal Space video that’s basically just history slop content, not citing any proper sources and propagating myths and misinformation as fact. The worst offender is probably the myth that the fountain that is found in the Court of the Lions was time-activated, with the only evidence for it being a clock being that there are twelve lion statues and there are two times twelve hours in a day.

Court of the Lions and its fountain in 2021. (Credit: Sean Adams, Wikimedia)

When we consider the archaeological evidence that exists so far, as well as the findings during the recent restorations, it seems clear that the marble block with its many holes through which the water entered the bowl was intended to diffuse the flow. Around the bowl we can see a corresponding poem of twelve verses by the vizier and poet Ibn Zamrak.

In verses 3 through 7 it specifically refers to “[..] which runs to that which is still, that we know not which of them is flowing”. This quite strongly suggests that the theme was similar to that of the many reflective pools that were so popular around the Alhambra and elsewhere. The idea of it being a time-controlled mechanism would thus seem to be a purely Western interpretation, barring some hitherto unknown evidence appearing.

Lossy History

Perhaps the most cruel aspect of history is that, much like time itself, it has no concern for those of us who live in the present. Throughout the eons as empires rise and crumble back into dust, wondrous inventions are made and soon again forgotten, leaving behind only echoes of deeds and wonder.

If we’re lucky some of it is recorded in a form as durable as Sumerian clay tablets buried underneath desert sands, but if not then what once was shall never be again. This impermanence is the eternal curse of the past, and also the reason why it’s always so important to make multiple copies of your important data.

Due to the passage of time history is mostly just ruins, pot shards and bones buried in mud and sand. Some will try to spruce things up with one’s imagination resulting in faux romanticism, but this naturally bears little connection to the past. That today the Alhambra has been largely restored is testament to how much more respectful we now approach the past, but the parts that were erased after the demise of the Nasrid dynasty are sadly likely to be lost forever.

Featured image: Reflective pool of the Court of the Myrtles, looking north towards the Comares Tower. (Credit: Tuxyso, Wikimedia)