A collection of more than fifteen papal documents here in English translation, spanning 160 years of clear and consistent teaching against particular errors that the Popes saw as mounting dangers in the 19th and early 20th century. 
 
Even a small sampling of these Popes goes a long way in showing that the same errors once condemned by the highest authority in the Church are now held and even taught as first principles in many sectors. Revealing.
 
For those especially who seek a deeper dive into the philosophical and theological roots of the current crisis - and on no less authority than the highest in the Church - this is an excellent resource.