Originally Posted by GW2Wiki

The Hall of Monuments is a location in the Far Shiverpeaks, part of the Eye of the North. It serves as a means to transfer player achievements from the original series to Guild Wars 2[1]. In the original series, players were able to display achievements, miniatures, prestige armours and prestige weapons in their Hall of Monuments. By "declaring an ancestor" using an in-game item[2] in Guild Wars 2, the player can link their two game accounts, granting them rewards based on their Guild Wars achievements. Rewards can be claimed by any character on the account[3], and can be claimed as many times as wanted but cannot be traded between players.

The rewards are known to include titles, companions, weapons, attire and miniatures[4]. These rewards are unique - there is no other way to get them. For this reason, their appeal will be mainly cosmetic; they will not give the player any huge advantages over other players[5]. It is unknown whether the number of items or achievements stored into each monument in Guild Wars will affect the nature of the rewards received.

New players to Guild Wars 2 will not be able to return to the original series and earn achievements for their Hall of Monuments[6]. The privilege is exclusively restricted to current players.