Food writer Leah Koenig goes back into the mists of time to explore the origins of matzah:
The Israelites’ earliest breads were unleavened flatbreads or cakes made of roasted barley. The word “matzo,” Joan Nathan writes in “The Foods of Israel Today” (Knopf, 2001), is likely derived from the Babylonian ma-as-sa-ar-tum, meaning “barley.” “The barley was ground with a flat stone; the stone was then heated with a flint stone until it was hot enough to cook the bread,” she writes. For centuries, these flat, rather tasteless cakes were the only “bread” the Israelites consumed. It was not until the Israelis encountered the ancient Egyptians that they learned about leavening.
The original matzahs were of course all soft and bendy, not hard like ours - and in some communities, such as the Yemenite community, they still are. This is why Hillel, in the Haggadah, makes a 'Hillel sandwich' with his matzah. While we struggle to put pieces of horseradish between two crumbly matzahs, he simply rolled up his soft matzah around his marror, just like a laffa.