Through the westernmost part of the Autonomous Community of Madrid
flows one of its most important rivers.
The river Guadarrama.
We follow the Geo-monumental Routes,
which receive funding from the Autonomous Community of Madrid.
They arose as a consequence of the results of the investigations
of the Geo-materials group of the Geo-sciences Institute
of the Scientific Research Council
and the Complutense University of Madrid.
They have always had the support of the Madrimasd Foundation,
through initiatives such as the Madrid Science Week
and the madrimasd website.
One of these routes leads us to the Regional Park of the Middle Course
of the River Guadarrama and the surrounding area,
protected due to its environmental interest and, in this case,
because it contains five bridges
which are symbols of the science which built Madrid.
Five bridges which exemplify the historic value
of an age in which connections
helped to establish Madrid as the capital of the country.
The geo-monumental routes are a project or an idea
which arose within the group of Petrology Applied
to the Conservation of the Heritage, of the Geo-Sciences Institute.
This group is composed mainly of geologists,
and what we do is study deterioration
or the materials which make up the Architectural Heritage,
especially that of the Madrid Region,
because we are located in the Autonomous Community of Madrid.
Through geological knowledge,
make people see that buildings are materials
and they were built by people,
it is not just the State or the Church which, with their money,
order the construction of a building in a certain age
and under the architectural patronage of the time.
It also means making people see
that traditional construction materials
played a very important role.
This journey along the river Guadarrama,
in the north-west of the Autonomous Community of Madrid,
has a number of stops, specifically... five,
where we will discover the representative bridges of that age
when the construction methods focussed
on facilitating the passage of people.
They are the Retamar bridge...
the Herrera bridge...
Alcanzorla...
Herreño and Rosario,
which now form part of the heritage
of the Autonomous Community of Madrid.
Some say that they are the most forgotten,
precisely because they have so often been used by the citizens.
A bridge is normally and indicator of civilisation.
The greater the degree of civilisation,
the more bridges they build.
In transportation routes, we have the paradigmatic example of Rome,
or the Middle Ages too, from the Romanesque on,
they are a clear reflection of the development of a society.
So, it is no coincidence that it was in the 16th century,
the time of the Renaissance, a time of splendour,
and then in the 18th century, which was the time of recovery,
from the Hapsburgs on...
that the construction of bridges was most developed, related,
of course, to the construction of roads
and the world of communications in general.
The current of the river Guadarrama carries us,
after passing through the most rugged area,
to the first stop, in the town of Las Rozas,
where a recreational zone has been created
around the Retamar bridge.
This is the most emblematic bridge along our route,
and it is an excellent example, to analyse and admire
the construction process of these engineering works.
And, if there is something which identifies all of them,
it is the material used in their construction: granite.
Following the general rule that you construct
using the materials available in the area,
the Madrid region owes part of its idiosyncrasy
to this plutonic igneous rock.
Many of its emblematic constructions are made of granite.
In particular one, responsible to a great extent
for the construction of the bridges under consideration here.
We are talking about the monastery of San Lorenzo de El Escorial,
testimony of another age and those who lived in it
and used it, as well as the bridges which surround it.
Madrid is a region in which there are many springs,
they are abundant here.
So, having that vital resource which is water,
without a doubt, was essential.
In any case, we must mention one aspect
which is never highlighted or is not highlighted very often
in the selection of Madrid,
which is that it was to get away from the Archbishop of Toledo,
who was indeed a tough nut to crack.
So, the power of the Cathedral of Toledo was so strong,
that moving to a city―which was not a little village in La Mancha,
as is sometimes said,
rather it was a well-organised, solid city,
with a large, comfortable, luxurious Royal Fortress,
and, at the same time, a place where there was no Bishopric
and there was no competition among powers,
for Felipe the Second that was an enormous advantage.
And, in addition, we also had the advantage
of having the granite quarries nearby,
which would supply the monumental architecture of Madrid.
People talk about all the factors which influenced
the designation of Madrid as the capital of the kingdom,
apart from all the religious, economic, historic
or strategic factors, which could be of interest,
also the existence of all those quarries
and all that extraction activity that existed,
all that knowledge of the treatment of stone,
was an essential factor in being able to raise a new city,
which would be the capital of the kingdom.
A number of bridges were built in order
to facilitate access to the monastery.
Without a doubt, granite made that possible.
However simple they are, they require engineering work,
particularly in areas of river courses
with large variations in the volume of water,
as is the case with the river Guadarrama.
Granite is a magnificent rock
to hold up any kind of structure,
because it has a high degree of resistance to compression.
In addition, it is impermeable, which makes it ideal
for constructions in contact with water for prolonged periods.
The granites which appear in these bridges,
despite having a very simple mineralogical composition,
which is quartz, feldspar and biotite, which is mica,
it is true that we can clearly differentiate two types of granite,
depending on the concentration of those three minerals.
When quartz and feldspar are present,
which are clear minerals, which we call leucocratic,
we will see a light granite,
sometimes with a slight yellow tinge,
due to the process of natural oxidation which it undergoes...
or the feldspar or the little biotite that appears,
that is why we call them leuco-granites.
On the other hand, if there is a predominance
of dark mica, biotite, or melanocratic mineral as it is known,
then it has a more greyish, darker tonality,
that is why we call them monzogranites.
These two types can be found...
on this bridge, mainly leucocratic,
which is leuco-granite, the light-coloured granite,
which comes from about four kilometres upstream.
On the other hand, on the rest of the bridges,
as we approach the Central System,
the Guadarrama mountains, they increasingly become more grey,
because the main form of granite is monzogranite, the dark granite.
One by one, we will discover five historic bridges
which, except the Alcanzorla bridge, maintain their original use.
First stop, the Retamar bridge.
As we mentioned previously, its granite construction
is fundamental to support its size.
Hence the powerful cutwaters.
Easily accessible, it still carries vehicular traffic, which,
trough sparse, is constant and almost without restrictions.
The infrastructure of a previous bridge was taken advantage of
and it formed part of the road from Galapagar to El Escorial.
In it, we can distinguish three types of granite,
two original ones and another which came later,
and the golden coloration of this stone,
mainly due to the oxidation of its minerals.
As you can see, it remains in a good state of conservation
despite anthropogenic action, which has now been eliminated,
and biological colonisation,
present in all the bridges to a greater or lesser extent.
We can see saline efflorescence, flaking, cracks and fissures,
as well as stealthy hunters
who have made the Retamar bridge their home, big or small.
On this one here, apart from the beautiful surroundings,
we can get a very clear view of the different construction elements
typical of a bridge, that's one thing.
And also, on this bridge,
specifically underneath, on the arches,
we can clearly see the typical alteration of granites,
that same alteration that we can see in nature,
we can see it here, to a great extent
because of work that has been done on the bridge.
The Retamar bridge is perhaps the most beautiful of all
because of its dimensions and its architecture.
It is the largest, with seven spans,
and the best cared for, in terms of the work carried out on it,
and the one which contains the largest volume of stone,
despite the fact that we are a long way from the granite outcrops,
which are four kilometres upstream.
But the architecture,
the physiognomy, the care in the quarrying,
which can be seen on many of the cutwaters,
the form of the cutwaters and the segmented crowns.
The sculpting, given that it is not so easy to work granite,
with that delicacy, to create a work of civil construction,
is perhaps a point in favour of this architecture of the 18th century.
Here, on the Retamar bridge, strolling around these places,
a number of ideas come into your head,
and one of them, for me, someone who works with stone,
is to see how this bridge has been worked,
how the surfaces have been made with different tools,
and also the wear, the erosion...
as Goya said, time also paints, time also sculpts.
All that natural texture,
the tremendous contrast it makes with the benches we have here,
the tables of the picnic area, which are also made of granite,
the same granite as that of the bridge, or very similar,
but, as they have been worked with mechanical means,
polished with polishers and cut with saws,
in the end they have a completely different appearance,
it appears to be a different material,
but no-it is the way it has been worked.
So, this also serves as a reflection on...
the fact that it is not only a question of using certain materials,
but also how we use them, how we work them
and how we transform them
in order to be able to incorporate them into our lives.
We follow the current of the river Guadarrama,
we say goodbye to the inhabitants of Retamar,
and we greet those who live near the Herrera Bridge.
Next to the Los Jarales housing estate,
and dating from the 16th century,
its construction was ordered by Felipe the Second,
once again, to facilitate access to El Escorial,
and as evidence of that, this engraving in the form of a grid
on the keystone of the bridge's only arch,
in clear, direct reference
to the form of the monastery, as tradition tells us.
It is in the Renaissance style
and designed by the architect Juan de Herrera, hence its name.
On its well-worn deck,
we can recognise some tracks of the stonemasons
and the marks left by the clamps
which held together the ashlars of the parapet.
At the entrance, we can also see two later boundary stones,
which indicated the monarch's hunting ground.
A number of later renovations,
related to the Torrelodones-Galapagar road,
led to the loss of the original drains
and compacting with cement mortar.
The growth of vegetation
is the greatest problem with this bridge,
as it makes it very difficult to see it properly.
There are even weeds growing up through its deck.
The Herrera bridge is very interesting,
there are marks of stonemasons, which can be seen.
The original paving of the bridge, with very large granite slabs,
is also interesting to see,
and how the original clamps, which are no longer here,
but the marks are still perfectly visible,
those clamps which held together
the pieces which comprised the parapet of the bridge,
it is interesting to see that.
At the Alcanzorla bridge,
what stands out, above all is the beautiful surroundings.
And, from the clefts in the granite
which is right next to the bridge,
we can see that blocks were extracted, to construct the bridge.
The Alcanzorla bridge is the next one, and perhaps the most peculiar.
It is believed to date from the time of Muslim occupation
and that it served to connect watchtowers.
With a little bit of imagination,
we can visualise what it was like when it was in use,
thanks to the row of granite blocks which is still conserved.
The Alcanzorla bridge,
also in the Los Jarales housing estate, in Galapagar,
stands in the most spectacular surroundings of the entire route.
In this case, it is easy to distinguish
the quarry from where the granites were extracted,
because it is right there.
In fact, if visitors looks closely,
they can see the quarrying cuts made back then-
there are many of them in the area around the bridge.
An aerial view reveals the gorge hewn through the granite
thanks to the action of the river and the passing of time...
The little that remains of this bridge is sufficient
to make out a base constructed
of granite blocks joined together with lime mortar,
in which there are up to three types of granite.
The state of conservation is particularly precarious.
Only the span remains,
but it is in very good condition thanks to excellent interventions.
Biological colonisation is evident,
particularly in the areas of mortar.
And, if nature continues its course without human intervention,
it will become more and more difficult to even see it.
Only one arch remains, which is the part of the intrados,
which is now propped up.
But it is the surroundings in which it stands
that makes these remains a site of such outstanding beauty.
We continue along the river Guadarrama
until we come to the next stop on our route.
It is the Herreño bridge.
It forms part of the "Royal Road from Madrid to Old Castile".
Built by Carlos the Third in 1784,
each day it carries heavy vehicular traffic,
perhaps the most striking thing about this veteran bridge.
On this stop,
we approach the village of Guadarrama from Galapagar.
What stands out is its robustness
and its powerful, pointed, "duckbill" cutwaters,
with a triangular cross-section of curved sides,
topped by segmented crowns.
The coping, which also has entrance and exit spaces,
is subjected to a large amount of traffic,
which has caused deterioration
and structural movements, with falls of complete blocks.
Vandalism, which is frequent here,
and biological colonisation,
are also among the main problems faced by the Herreño bridge.
Once again, flaking is evident,
with variations in the colour of the granite.
The surrounding area, of dense vegetation downstream,
is undoubtedly very beautiful,
but it also makes it difficult to view the bridge.
The Herreño bridge is perhaps the least visible of all.
The Herreño bridge is directly on the road,
the 510 road to El Escorial.
So it is covered, hidden by the very heavy traffic across it
and it is the great unknown.
It has the same architecture
as the Retamar bridge and the Rosario bridge,
because they are all from the 18th century,
and they are the connections which Carlos the Third made back then
to connect Madrid to the rest of the peninsula,
with the intention of creating a circular network,
a radial network of roads, as we know it today.
And it is the great unknown, but it also has its own charm,
in that it is a bridge which has survived to this day
and which continues to be used, like the Rosario bridge.
The Rosario bridge
is inside the village of Guadarrama, so it is inside a built-up area.
It has received some care and it is still in use,
because it is on the road leading to the mountains,
and there is plenty of traffic across it.
Small, but well cared for,
and it has a very characteristic physiognomy.
And so we come to the end of the geo-monumental route
of the bridges across the river Guadarrama.
And, fittingly,
it is in the village which has the same name as the river.
Here stands the Rosario bridge,
which forms part of the day-to-day lives of the villagers,
people and animals...
Today, it carries road traffic through the village,
in the past it was a connection between Granja de San Ildefonso
and the monastery of El Escorial.
Upstream,
the bridge is in an excellent state of conservation,
thanks to recent interventions.
Here, we find only one type of granite,
as well as a great deal of biological colonisation
and saline efflorescence,
due to the improper use of mortar in the past.
Vandalism, and also, in this case, graffiti,
present on the lower part,
has caused the loss of important parts such as the drains,
as we also saw on previous bridges.
The cutwaters, ready for possible rises in water levels,
are small, pointed and triangular, with curved sides,
and with segmented crowns.
Do the inhabitants of Guadarrama know
that beneath the wheels of their cars
there is a bridge from the 18th century?
Conservation work and raising awareness of our heritage
are once again fundamental if we want to continue to boast
of the civil engineering of the Autonomous Community of Madrid.
And experts in the matter
have a great deal to say about that maintenance.
When we study a building,
we study the materials of which it is made,
we always take one thing very much into account...
the building functions as a whole
and the materials in that building function as a whole,
so they cannot be individualised, considered separately...
of course they can be individualised, but...
there are many, many factors both intrinsic in the materials
and ones which are extrinsic to the material itself
and the building itself,
which favour or speed up that deterioration.
So, we cannot assign one form of deterioration
or a pathology we see in a building to a single cause,
we have to understand it in its entirety.
Simply put, in a building
the rock is subjected to compression and load-bearing stresses,
structural stresses, let us say, and, in some way,
even if the material is strong and resistant, they weaken it.
And then, moreover, if you take that material...
stony materials change with age,
in nature, we can see the weathering of the rocks,
due to the effects of atmospheric agents.
Well, that is also true of the materials in a building.
And what happens? Well, in a building, as I said,
there are many other factors, apart from weathering,
the water continues to act on the stone in the building.
So, well... what I said,
there are many different causes which favour deterioration,
and if the building is in an urban area,
the issue of pollution is an additional factor, let us say,
which, thank God, is not the case with these bridges.
It is inevitable that work will be needed or certain points
in order to combat certain problems.
Consequently, above all
the fact that the joints between the blocks start to open up.
That, as I said before, can lead to
the destabilisation of the entire structure,
so it is necessary to fill them in.
The work that was done in the last decade of the 20th century,
with the use of cement, was perhaps not the most appropriate,
because the use of cement,
as it is an excessively rigid material when it sets,
that causes not only the additional presence of salts,
which visually and structurally
damage the entire surface of the block,
but they can also open up the joints of those blocks,
separating them consecutively and structurally,
thus placing them in danger.
Visiting these vestiges of the past takes us back many centuries,
when the engineers began to create the network of roads of Madrid,
and the monarchs sought to adorn
the routes which they themselves used.
They are monuments which have blended into the landscape,
making it more human, more amenable.
And with so much human presence,
the expansion of built-up areas, that means that, in some cases,
there is barely a few metres separating
these witnesses of the past from much more recent constructions.
Even covering
what was the quarry from where the granite necessary
to build those bridges was extracted.
A bridge signifies many things, but, above all,
it is a symbol of mankind's determination to overcome nature.
In reality, we are taking advantage of the resources of nature,
we are, necessarily, living alongside it,
but we are also trying
to remove all the discomforts that nature presents.
So, with bridges, tunnels,
roads, constructions... what we are doing is trying,
when it comes down to it, to humanise the territory,
which was pre-human,
convert it into something which we can move across,
which we can inhabit, and provided that is done as it was then,
in a balanced way, using the natural materials themselves,
and also in a contained manner...
in the end, human intervention forms part of that territory.
What is bad is what we are doing now,
which is clearing everything away,
so that nature does not inconvenience us in any way,
even if we preserve it in some isolated places,
to do without nature, to turn our backs on it.
This geo-monumental route
of five historic bridges in the Madrid Region,
leads us to discover the human impetus
to make travel as easy as possible,
seeking to overcome the complications presented by nature,
in this case, the river Guadarrama,
and, why not, to be witnesses to the work
of those who constructed some of the finest examples
of civil engineering in the Autonomous Community of Madrid.