(Obviously) I'm no expert, but I've always been interested in Roman/Byzantine history and the crusades however I cant quite figure out why the templars ended up attacking Constantinople in 1204.
Here's a previous answer I wrote about this:
Why was Constantinople sacked in 1204?
But I should also note that the Templars weren't involved in the Fourth Crusade at all. I suppose there might have been individual Templars there, but I can't think of any examples; in any case, the Templars, as a group, were not part of the siege.