A recent application for Serial Nomination of Viking Sites by Icelands Thingvellir to the World Heritage Convention has included the following comments:
Although a number of medieval assembly sites are known in other European countries, particularly in Norway, Þingvellir is historically, archaeologically and symbolically the most significant. In other countries, the assembly sites are those of local or regional assemblies that performed a different role. The Althing as a general assembly represented the whole country and was in effect the capital of Iceland for two weeks each year where key legal and administrative decisions were made.
Þingvellir has more visible remains than any other thing site, and there are indications of very rich archaeological layers yet to be explored. No other sites show visible ruins, although mounds are extant at the Tynwald in the Isle of Man, Gulating and Frostating in Norway, and at the Thingmount in UK. In addition to physical remains and national status, the Althing site at Þingvellir in Iceland has extra values connected with its long history of continued use, documentation and knowledge of its governance role, transmitted down the centuries in the Icelandic sagas, and through its dramatic natural setting which has changed little since the 9th century. It has thus acquired symbolic associations with Icelandic identity and with Norse culture and is perceived as a place of outstanding aesthetic value.
The Althing is thus unique through its extensive built remains, its unspoilt setting and for its strong and well known associations with Germanic Law and Norse culture.
The Full Unesco Document can be read here