These weapons are very old, and very powerful. They are often of diamondplate, and sometimes of alaricite, that ultimate metal, and are worked exquisitely. Each Great House and many Ducal houses are in possession of one of these weapons, and the weapon itself lends validity to the noble line of the House it protects.
The story goes that these are weapons claimed from war chiefs of the enemy during the so-called Elven War. When the fires were put out and the Compact began rebuilding, entire families, tribes, and fiefdoms had been destroyed. Those that earned glory in battle, claiming these swords, became the noble Houses known today.
Traditionally, each House appoints a skilled wielder for these weapons, granted the title "Sword" - despite the form the actual weapon might take. This is a revered position, and it is expected that a Sword would never use the House's heirloom weapon for personal glory, or personal vendettas. To do so is a grave insult to the history of the weapon, and almost always results in the offender being stripped of the title (and the weapon it represents).
Heirloom weapons are the best weapons in Arvum, and they are held to defend the Houses from mortal peril - not to win tournaments, or duels. The exception would be if two Swords were to duel in order to prevent two Houses from going to war.