Tech Archaeology:
Sri Lanka's Sigiriya rock citadel probed with hi-tech tools
At Sigiriya, in central Sri Lanka, a group of geophysicists are probing the ground around an ancient rock fortress with ground penetrating radar, looking for man-made structures which are 1,500 years old.
"We have already detected possible prospects," says geophysicist Nalin de Silva, who works for Sri Lanka's Geological Survey and Mines Bureau.
The Bureau is using techniques normally used for prospecting minerals to help the island's department of archeology explore the grounds around the Sigiriya fortress, which the United Nations has designated a 'world heritage' site. 
Sigiriya was built during the fifth century by Sri Lanka's King Kasyapa I, who feared an attack by his half-brother Mugalan. Kasyapa seized the crown by killing their father, Datusena.
The site is known for frescoes of beautiful maidens painted on the impossibly sheer rock face that can now only be reached through an iron stairway. Kasyapa built his palace securely on top of the rock.
But he is said to have perished in combat with his half brother on the plains below, having reigned for 18 years.
The rock is surrounded by a landscaped patchwork of shallow ponds - a water garden - which is irrigated by a complex network of waterways and trimmed with fountains.
Ancient Sri Lankans who built large reservoirs - called tanks - are known for their feats of irrigation engineering, which were vital for their agriculture based civilization.
The enraged and fratricidal Kasyapa is said to have walled his father into the bund of Kala Wewa, a large reservoir after finding out that most of the funds of the royal treasury had been committed to building the tank.
Unexplored
Only a part of the structure on the grounds around the citadel in Sigiriya (Lion Rock) have been explored and restored.
In a plateau like landing halfway up the rock, the giant paws of a lion carved from the rock, still remain.
"The aim of the current phase is to map the man made structures in a 100 metre stretch at the northern section of Sigiriya’s Western entrance," says de Silva.
The team will later conduct a geo magnetic survey to find long-buried artifacts. Magneto metres can point to buried objects by measuring changes in the strength or direction of a magnetic field in the ground.
The team will also use another technique called electrical resistivity imaging (ERI) to find possible underground structures. Impulses sent into the ground by electrodes inserted through bore holes allow the team to map differences in subsoil.
Soil, rock and iron tools, have different resistivity characteristics.By analyzing the variations, possible sites for archeological digs can be located.
Silva says archaeologist believe Kasyapa's garden extends toward the Eastern section of Sigirya as a moat that runs around the fortress is located further away from the rock in that area.
The head of the Geological Survey and Mines Bureau, N P Wijayananda says the techniques will be used at other unexplored archeological sites in the country, if the pilot project in Sigiriya is successful.
(Source: LBO – 10 Sept, 2009)