That rascally fig tree

Posted on March 4, 2010

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We have one serious enemy in our attempt to preserve the spring chamber and spring gallery of the Aqua Traiana.

More stubborn than the nuttiest old archaeologist, more rapacious than the Emperor Trajan himself, is a certain damned fig tree, sitting adjacent to the ‘church’ chamber itself, from where it sends its roots down into the ‘spring’ chamber or ‘water capture’ chamber and down into the aqueduct.

The spring chamber was lined with rock-hard waterproof hydraulic cement, and that cement was painted with Egyptian blue paint – paint which gives us a sure and certain date for the construction of that chamber.

Unfortunately, since the spring chamber was drained, there is now a layer of roots between the painted roman cement and the structure of the wall.

Fig trees are one of the greatest enemies of ancient monuments.  The day that your doctor told you that eating figs is a great source of Calcium and gives you strong teeth and finger nails, you might have guessed that fig tree roots absorb lots of Calcium from the soil.  You’d have been right!

Root-tips are covered in bio-films which help them absorb mineral nutrients, and through that film, through either clay or hetrotrophic bacteria, H+ Hydrogen Ions are exchanged with Metal Ions, such as Ca2+ Calcium Ions in mineral fragments.   It’s called Bio-mobilisation.

Diagram of Fig Tree Roots

Calcium hungry fig tree roots sucking the strength out of the Roman Hydraulic Cement

So those cheeky fig tree roots have been busily sucking all the Calcium out of the rock-hard hydraulic cement, so that it’s no longer hard at all.  In fact it’s distinctly friable and crumbly.  Recently, we had to keep our mouths closed and grind our teeth as we watched a VIP guest break off a big chunk of the hydraulic cement and crumble it between his fingers.

We would like to see the Roman Hydraulic-Cement preserved.  It is a significant technical component of this unique remaining example of roman engineering, and if we lose it, we also lose the Egyptian Blue paint – which was so expensive that it proves that this location was a place of great importance.

So a key question is how to preserve this hydraulic cement or ‘intonaco’.   It is possible that the live roots are currently holding the intonaco in place.  Eventually the destructive fig tree needs to be removed, but if we kill the tree and the roots die, the intonaco could just drop off the walls and crumble on the floor.

Two days ago I met the young owner of the site for the first time.  He is eager to clean up the place, and be seen to take good care of it.  He wants to cut down the fig trees – in fact, he may already be doing so.

To stop and think, or to go for it?  To be or not to be?

To take a chain saw to that cheeky old fig tree, or to leave it standing?

That is the question.

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