The Acta Apostolicae Sedis or Acts of the Apostolic See (in English) is the official gazette of the Holy See, functioning like the official gazette of any government or state around the world. In here, one finds encyclicals, official decisions, appointments, etc. The gazette was established in 1908 by Pope Pius X and has been published every month since then.
Just on the face of it, this is very interesting to anyone that enjoys such things. However, what is particularly fascinating and an excellent source for those of us in the chivalric/heraldic world is that all those who have had the honor of being admitted into any of the papal orders are mentioned in the gazette. In other words, this resource is a quick and easy way to validate whether someone who claims to be a, say, Knight of the Order of St. Sylvester really is so.
As most of those that are involved in orders of chivalry, there are many (way too many) false orders and even more pretenders that claim to have more knighthoods than even the King of Spain! A very (un)healthy market has been the sales of false membership into papal orders. This has gone on for a long time and a few years ago was wildly popular. Naturally, this was completely false and many people were taken in as victims of these scams.
The availability of the Acta online is a veritable boon to all those who like to validate such claims.
The link to the online archive of every single publication of the Acta Apostolicae Sedis since 1909 is: http://www.vatican.va/archive/aas/index_en.htm
I’d like to thank Dr. Charles Drake for alerting me to the existence of the archive!
Note: image from Wikipedia