Burgos castle siege tunnels & well

Burgos well drawingAmongst the most interesting features of Burgos castle are the medieval well, siege tunnels and counter mines that have been preserved below the surface. The well was dug in order to provide a reliable water supply for the castle in the 12th or 13th century and was excavated deep into the bedrock on which the castle was built.Burgos well shaft

The main well is some 1.7 metres wide and goes down 63.5 metres until reaching the natural water table underground at this depth. Castle wells are not unusual on a European level although in Spain water storage cisterns both below ground and above ground to collect rainwater are just as common as wells. What makes the Burgos well special though is the ashlar spiral staircase that runs alongside the well, deep into the ground, to provide maintenance access to the deepest part of the well.

The well shaft itself has been lined with finely cut ashlar blocks for the whole depth and include slits at regular intervals that provide a degree of natural light from within the well shaft into the adjoining spiral staircases that otherwise would be completely devoid of daylight.

If the presence of a deep spiral stair alongside a well shaft wasn’t remarkable enough, the arrangement of these stairs is exceptional. Burgos pozoThe spiral stair and well shaft were constructed as a single engineering project with the ashlar blocks cut from a single block of stone where the curve of the stair and the well shaft meets. The stairs are constructed in six stages, each one about 10 metres deep, with a connecting corridor at each stage linking to the next length of spiral staircase.

Each of these six connected lengths of spiral stair change direction at every level so a person travelling to the lowest level will go down from the surface to the first level in a anticlockwise direction, cross the short corridor to the next stair and then from that level to the next the spiral is reversed and continues the descent in a clockwise direction and so on through all six levels.

Burgos spiral stairThe purpose of this change in direction of the spiral isn’t certain but it may simply be an ingenious device for preventing someone descending quickly from becoming dizzy and disorientated in the darkness. By changing the direction of travel mid way in a descent where you can’t see the bottom and is poorly lit, could help the person know their relative position along the length and thereby help them gauge how much further they need to travel. In addition, the linked corridors at each level, with access slits into the well shaft itself, will allow maintenance and inspection of the shaft at regular intervals.Burgos countermineentrance

A further remarkable aspect of these subterranean stairs are siege mines and counter mines that were tunnelled through the rock in order to reach the wells and cut off the water supply to the castle.

It is not certain at what date these mines were cut. A strong possibility is that they date from 1475 when Burgos was laid at siege for eight months during a succession dispute between Isabel the Catholic and Juana la Beltraneja over the crown of Castile. They may be much older than this though.

Burgos siege tunnelThe siege tunnel is started from outside the castle perimeter where it travels under the curtain wall at some depth heading in the direction of the main castle well and water supply. The tunnel itself is surprisingly high and wide and allows a man to proceed more or less unhindered, perhaps having to stoop a little depending on his height.

At some point during the tunnelling operation, the defenders of Burgos castle became aware of the work and commenced a counter mine in order to reach the attacking mine and prevent further progress. These counter mines are also of significant proportions and together, both attacking and defending mines meander through the rock until meeting at a point 14 metres below the surface. Steps have been cut into the rocky floor of the counter mine to enable a steep and rapid descent.Burgos tunnel

The engineering effort to dig these tunnels and to remove the rock from them as they progressed would have been substantial. It is not known how long these works took to complete or what any outcome may have been. They could be the result of several different campaigns separated by many years. It is possible that one of the tunnel chambers was created as a deliberate postern exit route connected to the siege tunnels. This would allow occupants of the castle to make a covert exit using the well shaft stairs into the tunnels and away. Burgos tunnel drawing

The survival of these medieval tunnels however is significant as very few siege works survive and especially not to such a large extent. The tunnels are open to visitors of Burgos castle with several guided tours available on selected days. These visits must be booked when arriving at the castle entrance for which an additional although modest charge is made.





Photos on this page: From top: Well, drawing; well shaft; graphic showing well & spiral ashlar blacks; top of spiral stair to well; entrance to countermine; mine tunnels x2; graphic showing tunnel positions.