The valley of Bulgaria's Thracian kings may be larger than believed and its extent may touch even the town of Sliven's borders, the famous Bulgarian archaeologist Professor Georgi Kitov said Monday.

Professor Kitov's team of scientists and archaeologists will start excavations of 15 Thracian tumuli in mid July as according to their preliminary research they contain many unique artefacts.

"All of the tumuli have been already pillaged by treasures hunters, but I really hope they did not know what to look for," Professor Kitov said.

It is expected that the excavations continue three months and they will cost around BGN 200 000.

At the end of June a team of the Discovery Channel will come to Bulgaria to make a documentary for the excavations.