Crusaders captured Tripoli in 1109 butchered the defeated Muslims, and destroyed the Banu Ammar library, at that time, the finest Muslim library in the world. About 100,000 books - deemed impious - were burned.

In the sack of Constantinople in 1204, the Crusaders destroyed the last surviving copies of classical works in Europe.

It is “ironic !!!” that Persian scholars had “converted” to Islam and saved as much ancient knowledge as they could by translating it into Arabic and this was then finally destroyed leaving nothing in Europe. This is why the Dark Age took hold.

The city fell on July 12, and was sacked by the crusaders. One hundred thousand volumes of the Dar-em-Ilm library were deemed "impious" and burned. The Egyptian fleet arrived eight hours too late. Most of the inhabitants were enslaved, the others were deprived of their possessions and expelled. Bertrand, Raymond IV's illegitimate son, had William-Jordan assassinated in 1110 and claimed two-thirds of the city for himself, with the other third falling to the Genoans. Thus Tripoli became a crusader state; the rest of the Mediterranean coast had already fallen to the crusaders or would pass to them within the next few years, with the capture of Sidon in 1111 and Tyre in 1124.MediterraneanSidonTyre References

When the crusaders captured Tripoli in 1109, apart from butchering the defeated Muslims, they destroyed the Banu Ammar library, at that time, the finest Muslim library in the world. About 100,000 books of Muslim learning were cast into the flames. In the sack of Constantinople in 1204, the western crusaders destroyed the last surviving copies of classical works in Europe. [4][4] The city fell on July 12, and was sacked by the crusaders. One hundred thousand volumes of the Dar-em-Ilm library were deemed "impious" and burned. The Egyptian fleet arrived eight hours too late. Most of the inhabitants were enslaved, the others were deprived of their possessions and expelled. Bertrand, Raymond IV's illegitimate son, had William-Jordan assassinated in 1110 and claimed two-thirds of the city for himself, with the other third falling to the Genoans. Thus Tripoli became a crusader state; the rest of the Mediterranean coast had already fallen to the crusaders or would pass to them within the next few years, with the capture of Sidon in 1111 and Tyre in 1124.MediterraneanSidonTyre References

The Fall of Tripoli to the Muslim Mamluks. The battle occurred in 1289 and was an important event in the Crusades, as it marked the capture of one of the few remaining major possessions of the Crusaders. =1616