Lla Sessiwn Gemruis, earlier known as Sessiwn Kemres, can be described as "a group of people interested in Kemr and in the Brithenig language". Originally, the Sessiwn was precisely that: a small group of people centered around Master Smith who enjoyed discussing these two things. Gradually, the group grew larger and larger and so did the scope of the discussion. Thus, Kemr became the centre of an alt-history that did not only affect the British Isles but also other parts of the world, and voilà, Ill Bethisad was born!
The "old" Sessiwn was active in the years 1996-1999. During that period, the traffic consisted solely of CC-ed emails between the people on top of The List. In 1999 the group moved to a mailing list, Celticonlang, and later to the Conculture list, where it grew further into what IB has ultimately become. The archives of this old Sessiwn can be found here: http://mercury.ccil.org/~cowan/sessiwn/ .
In January 2005, Andrew decided to revive the Sessiwn (under the name Sescam, from Sessio Cambriensis) as a Yahoo! group. The group once again focuses on the Brithenig language and the British Isles within the framework of IB, and can be seen as an adjunct to the group. Its address is: http://groups.yahoo.com/group/sescam/ .