The chart that Alayman references in post #9, that comes from the "Trail of Blood" booklet, lists a lot of medieval groups but there is no documentation to show that they were Baptistic. The Montanists believed in new revelations after the completion of the New Testament, they had women preachers, they were similar to modern charismatics. Novatian, founder of the sect of that name, was "baptized" by pouring because he was sick at the time - not a very good role model for Baptists. The main issue between the Donatists and the Roman Catholics was that Donatists rejected the validity of sacraments performed by unworthy clergy, while Roman Catholics insisted that such sacraments were valid. (Today, most IFBs would side with the Roman Catholics on that particular issue - very few if any IFBs would reject baptisms performed in the churches of Jack or Dave Hyles based on the moral turpitude of those pastors).
The famous Baptist historian Robert Robinson, in his book "Ecclesiastical Researches," published in 1792, states that many of the "Baptist" groups that are now claimed in our Baptist chain of title were Anti-Trinitarian. Robinson, who was Anti-Trinitarian himself, thought that was a good thing. (If his name rings a bell, he was the author of the hymn "Come Thou Fount of Every Blessing)."
I accept the Waldenses as Baptistic, probably the Henricians and Petrobrussians also. The Albigenses may have been identical with the Cathari, who were totally heretical Manichaeans. "Anabaptists" was a catch-all term used to describe any groups that rebaptized converts for any reason, by any mode - groups that were branded as Anabaptists by their enemies may or may not have been Baptistic - nowadays the Jehovah's Witnesses and Morons, who rebaptize, would be classified as Anabaptists, but that does not make them Baptists. Nor does baptism by immersion prove that any group is thoroughly Baptistic - up through the 16th Century, many Catholic and Anglican baptisms, and all Greek Orthodox baptisms, were performed by immersion, but that does not make those groups Baptist. Unfortunately, some Baptist histories make all sorts of claims of kinship for these medieval sects, for which no documentation is provided. I suppose we can call it "The Joy of Sects."
I hold to the principle that there have been Baptistic groups through the ages, but there is absolutely no documentation to demonstrate any sort of link-chain succession. Not even close to it. And even those groups that appear to have been Baptistic did not always believe or practice the same way as modern IFBs today. I, in common with Alayman, am "freaked out" by the claim of a chain link from John the Baptist to the present day. Milburn Cockrell of Berea Baptist Church in Mantachie, Mississippi, in his book "Scriptural Church Organization," reprinted the familiar Trail of Blood-style chain of title, but he inexplicably ends up at a church in Oakland, California with no mention of Tennessee. I don't recommend or endorse that book, but those who want to research the "D" position of "Unbroken Succession" can check it out in that book. The problem with those who hold that position is that they will say "If your church is not in that chain of links from the time of John the Baptist, then it is not a true church" and then they will try to take over your church and have the pastor re-ordained in their clique and all the members rebaptized. That is an extreme position that freaks me out too, but in my opinion most Landmarkers today do not hold to such an extreme notion. (Note - if you ask the churches that hold to "Link Chain Succession" to document their own place in the chain of title back through the Middle Ages, they will tell you "We don't have that information - the Catholics destroyed all the records)." In theory, if no link-chain can be documented, then there can be no true churches today - that was the position of Roger Williams, who planted a Baptist church in Rhode Island in 1639 and then abandoned it after a few months, saying that there were no true churches on earth with the authority to serve as a "mother church."