Saturday, in Istanbul once more. A group of ANCH students opted to visit the conservation laboratory associated with the nearby Yenikapı site. Here, in 2004, as excavations for Istanbul's underground metro proceeded, workmen encountered the remains of a long-lost harbour.

Further excavation revealed the sunken remains of over 30 ships from Constantinople's commercial harbour, the Harbour of Theodosius, which had been in use between the 5th and the 10th centuries AD.

Remarkably, the wood of the vessels had been well preserved thanks to the anaerobic conditions. Istanbul University's current project (in conjunction with the Underwater Research Institute in Bodrum) is to conserve and analyse the substantial elements of keels and hulls that have come to light, as precious remains of a trading world now largely lost to us.

With one of the postgraduate students from Istanbul University as our guide, we visited the excavation site itself. Then we proceeded to the laboratories, which comprised a basic workshop surrounded by long tanks filled with purified water. Here we learnt about the conservation process (which may take several years!), we watched the careful photographic work being undertaken, and we were shown the final computer reconstructions of one of the boats.

And what of the goldfish? We saw the goldfish as we viewed a late stage in the conservation process: just before the lengths of wood are lifted from their purified water baths for photographic analysis. As they swim unconcerned around these ancient timbers they perform a valuable service: ingesting unwelcome bacteria, they assist in maintaining the purity of the water bath, so important to the preservation of this valuable evidence.

Our warmest thanks to Professor Sayar for making this visit possible and to the conservation unit at the Yenikapı site for giving up their time to speak with us.