capital of the Khmer Empire had changed back to the plains north of the Tonle Sap-lake, more temples were built at the site of Koh Ker. An inscription mentions the reign of Udayadityavarman I in 1001. At the beginning of the 13th century the last sanctuary was realised there. Under Jayavarman VII, the Prasat Andong Kuk, a so-called hospital-chapel, was built, one of more than 100 of hospital-sanctuaries built under this ruler. History of research 19th century In the second part of the 19th century, French adventurers ranged the forests around the site of Koh Ker while hunting game. They brought word of the structures in the area back to France. The French researchers Lunet de Lajonquière and Étienne Aymonier came to Koh Ker. They saw the main temple-complex Prasat Thom/Prang, the Baray and a group of linga-shrines. They also discovered a few subsections of a chaussée (i.e. highway) with a breadth of more than . They supposed that a road once connected Koh Ker with Wat Phu (today in southern Laos). Around 1880, members of a French expedition arrived at Koh Ker and looted numerous statues and reliefs. These pieces are now in the Musée Guimet in Paris. 20th century At the beginning of the 20th century, art historians realised that a full-fledged style was developed at Koh Ker. Georges Coedès concluded from inscriptions that Koh Ker was capital of the Khmer empire (928 – 944 AD) under the reign of Jayavarman IV and his follower Harshavarman II. In the 1930s, again French researchers came to Koh Ker. They discovered numerous monuments and counted fifty sanctuaries in an area of . Henry Parmentier made a number of drawings. After an interruption because of the reign of terror of the Khmer rouge, research at Koh Ker continued by APSARA, French, Japanese and Australian scientists. 21st century At the beginning of the 21st century, scientists concluded that not all of the monuments could have been built in the short time when Koh Ker was capital of the Khmer empire (928 – 944 AD). A new era started at Koh Ker as photographs made by satellites were analysed. In 2004 the protected area was extended to . For five years, Japanese researchers explored and described 184 monuments, including documenting their exact locations. The Australian researcher Damian Evans and his team were able to verify Lajonquière's theory that there once was a Khmer