Answer:
1.because the roman empire up until that point was the most successful European based nation. and since it collapsed everything got worse in Europe.
2.because pope innocent the 2nd or 1st cant remember promised that all of the Europeans sins would be forgiven if they took up the cross
3. because it showed you would invest heavily in your devotion to god and the pope.
4.gothic archways which were also used on castles
5.since literary rates dropped you were engaging in an act of chivalry by keeping records of kings and other people.
