Mardi ibn Ali al-Tarsusi
Mardi ibn Ali al-Tarsusi was a 12th-century Ayyubid-era writer and expert on military matters. He wrote a number of treatises, including a military manual for Saladin in 1187. His writings have proved an invaluable resource for medieval and military historians.
The well known treatise was entitled Tabsirat arbab al-albab fi kayfiyat al-najah fi al-hurub min al-anwa' wa-nashr a'lam al-a'lam fi al-'udad wa-al-alat al-mu'inah 'ala liqa' al-a'da' , or "Information for the intelligent on how to escape injury in combat; and the unfurling of the banners of instruction on equipment and engines which assist in encounters with enemies."
The first clearly written record of a counterweight trebuchet comes from Tarsusi, who wrote a military manual for Saladin circa 1187. He describes a hybrid trebuchet that he said had the same hurling power as a traction machine pulled by fifty men due to "the constant force [of gravity], whereas men differ in their pulling force." (Showing his mechanical proficiency, Tarsusi designed his trebuchet so that as it was fired it cocked a supplementary crossbow, probably to protect the engineers from attack.)
In his book, Medieval Siege, Jim Bradbury extensively quotes from Tarsusi concerning mangonels of various types, including Arab, Persian and Turkish, describing what could be trebuchets, but not quoted as above. In On the Social Origins of Medieval Institutions, more detailed quotes by Tarsusi may be found on the various types of trebuchets.