We know that by the time of the Second Crusade Al-Qalanisi was eighty four years old, so he would have already been a mature age by the time of the First Crusade. Although he does not appear to have taken part in any combat with the Crusaders, his Chronicle is especially interesting because it presents a contemporary account of the Crusaders as they were understood in Damascus, from the beginning of the Crusades until his death on March 18, 1160. The full title of his work is the Continuation of the Chronicle of Damascus, which reveals it was intended as a supplement to an earlier work.
The importance of the Damascus Chronicle comes from the fact that it is one of the primary sources of nearly all following arab historians of the Crusades. For example, it was extensively cited in the later works of Sibt Ibn al Jawzi, Ibn Al Athir, Abu Shama, and Kamal Al-Din. The work is especially unique in the way it traces the hardening of Muslim feeling against the Crusaders and the eventual unification of Muslim peoples up to Nur-Ad Din. The work also includes a well known and often quoted description of the destruction of Jews by Crusaders upon conquering Jerusalem in 1099. He wrote,
The defenders were driven down, and the Franks stormed the town and gained possession of it. A
number of the townsfolk fled to the sanctuary [of David] and a great host were killed. The Jews
assembled in the synagogue, and the Franks burned it over their heads. The sanctuary was surrendered
to them on guarantee of safety on the 22nd of Sha'ban (14th July) of this year, and they destroyed the
shrines and the tomb of Abraham.(1)
For a lengthier overview of the life of Ibn Al Qalanisi, see the introduction in H.A.R. Gibb. The Damascus Chronicle of the Crusades: Extracted and Translated From the Chronicle of Ibn Al-Qalanisi. London: Luzac & Company, 1967.