Where to Find Free Church History Books and What to Watch Out For
You can find Libro Historia De La Iglesia Cristiana Gratis sitting scattered across a dozen different websites. Some are legitimate archives, some are just PDF dump sites with broken chapters. The problem isn't availability. It's quality control and which edition you end up reading. The most commonly referenced work in this category is Philip Schaff's History of the Christian Church. It covers everything from the apostolic age through the Reformation in eight massive volumes. There are also shorter single-volume surveys by historians like Jaroslav Pelikan and Henry Chadwick that occasionally surface on archive sites. When I was looking for a complete free text a few years ago to cross-reference some dates on the Nicene Council, I hit a wall pretty quickly. Most of the "free" versions were either truncated or stripped of footnotes entirely. The full Schaff set with all the marginal references was only available on Archive.org in a fully OCR'd format that sometimes misread Latin citations as random characters. The workaround I ended up using was downloading the Internet Archive version and then comparing problematic passages against the Google Books preview of the same edition. It took longer than just getting a clean PDF, but the footnote references actually matched up. If you need something faster and less reference-heavy, the Pelikan volume that occasionally circulates on Z-Lib or similar repositories is a reasonable trade-off.
Another issue people don't expect: the public domain cutoff. Schaff died in 1893, so his main work is free to distribute in most jurisdictions. But many of the supplementary essays, maps, and indices included in later editions may have different copyright statuses depending on when they were added. I ran into this with a site that bundled a 1920s commentary appendix with the main text. The free distribution was technically fine, but anyone citing it academically would need to separate the two materials. Project Gutenberg has selected volumes from the Schaff series, though not all eight. They also carry older works by Ecclesiastical historians like Edward Gibbon's chapters on early Christianity, which you should treat as supplementary rather than primary reference material since his bias toward pagan sources skews the narrative in places modern scholars no longer accept. If you are doing serious research rather than casual reading, I would recommend keeping a formal library subscription alongside whatever free sources you find. The paywalled academic editions of these texts have corrected typographical errors, restored missing passages, and include cross-references that the free versions lack. A free copy is fine for a first pass. It becomes a liability when you are writing something that needs citations you can stand behind.
