there are a number of books and articles on the bowie blade, and few of the agree on its story. One of the best was a 3 or 4 part series on one of the knife collector magazines a few years back
. Bowies's brother Rezin sorta capitalized on James fame and created part of the legend, including several presentation "bowie knives" that are authentic "bowie knves", just form the worng Bowie.
Much of the rest is second or third hand reports from someone who "knew" long after the facts and fails even minima historical standards of credibility. I base my own opinion,
and thats all it is, on the few survivors accounts, and even they had their own bowieknives to grind.
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Basically he was incapacitated and deathly ill, of typhus or typhoid as I recall, and was being tended by a servant from his Tejano-wife's family. Very shortly after Santa Ana's forces arrived he ceased having any role in the command structure leaving Travis in sole "command". Accounts of his death are circumstantially suspicious. I
personally believe he was probably dead of his illness before the fall of the fort and the ensuing massacre, but that only my own conjecture.
Remember that after the event all of the fallen Alamo defenders were immediately raised to the Pantheon of Texas civility. Their survivors/families were given large land grants by the new Republic, which really skewed documentable historical facts; starting frauds and feuds, some of which are still ongoing.
I imagine that his blade may have fallen into the hands of a Mexican soldier, but by that time the "bowie-knife" fad had taken off and there were probably dozens of bowie-style, oversized single edged hunting knifes with some sort of hand guard in the hands of the "anglo" defenders. Perhaps in his later years he may have had a more ornate version made, but no evidence has ever surfaced of such. If his was picked up by someone it was not recognized, and in the decade after the founding of the Republic, it, Travis's sword and pistols, Crockett's rifle (whole 'nother tale for that'un) would have been the Holy Grails of Texas Culture. the fact that they have not surfaced is pretty indicative I think.