Board games have been played in most cultures and societies throughout history; some even pre-date literacy skill development in the earliest civilizations. A number of important historical sites, artifacts and documents exist which shed light on early board games.
Senet has been found in Predynastic and First Dynasty burials of Egypt, c. 3500 BC and 3100 BC respectively. Senet is the oldest board game known to have existed, having been pictured in a fresco found in Merknera's tomb (3300-2700 BC)
Mehen is another ancient board game from Predynastic Egypt.
Go is an ancient strategic board game originating in China
Patolli is a board game originating in mesoamerica and played by the ancient mayans.
The Royal Tombs of Ur contained, among others, the Royal Game of Ur. They were excavated by Leonard Woolley, but his books document little on the games found. Most of the games he excavated are now housed in the British Museum in London.
Buddha games list is the earliest known list of games.
What's it worth? Take a look at this Payday Board Game price guide: sold listings for a value indication.