At the massive, brick castle "Malbork" in Poland, see four of the Grand Masters of the Teutonic Knights, the group that built it. Overview at www.angelfire.com/mi4/polcrt/malbork.htm. A bare-bones narrative summary of their history is at www.heraldica.org/topics/orders/teutonic.htm.
Overview of crusades and Templars - see the History of Central Europe at http://mysite.du.edu/~etuttle/misc/europe.htm#Mong.
During the crusades, Teutonic Knights hospitals and otherwise helped and protected the pilgrims and the wounded. When the crusaders lost the Holy Land back to the Saracens, there was no more of that same protective and healing work to be done there. See the pictures and narrative at www.crystalinks.com/teutonicknights.html. See also James Michener's large novel, "Poland." Review at www.allreaders.com/Topics/Info_1544.asp. See the portions on the slaughter of Christians by "Christians."
So they retreated to Venice, built up their economic and political fortunes, and then from there, morphed into mercenaries. They killed Baltic Christians as "infidels" just as they killed other nonbelievers, on grounds that they had to have been converted to Christianity by the Pope's forces and not some earlier saint who did not count. See remus.shidler.hawaii.edu/genes/WPrussia/Teutonic/home.htm.
In other ways, they were a jolly group, says this site, noting their camaraderie and sense of humor. See department.monm.edu/history/urban/articles/humor_of_Teutonic_Knights.htm. Similarities to Chaucer and Boccaccio are shown there.
See Poland Road Ways for posts and cites to Malbork and the Teutonic Knights. The Roman Catholic view is at www.newadvent.org/cathen/14541b.htm.
The Knights are still active. I found a website with a large portrait of Pope Benedict at the top left of the page, and the history and recruiting efforts discussed, modern day opportunities for service. Still looking to find it again.
They founded Brasov, Romania, where the castle named "Bran" is tourist-featured as a place where Vlad Tepes (the Impaler) is said to be associated. See www.maisnie-champenoise.org/uk/teutons.html. See Bran Castle at " Romania Road Ways - Vlad Tepes.
There is a digitalized copy of the F.C, Woodhouse 1879 book, "The Military Religious Orders of the Middle Ages," online. Do a search for modern Teutonic Knights