stately libraries
justice halls became useless
no longer revered
… the stately libraries and halls of justice became useless to an indolent generation, whose repose was seldom disturbed, either by study, or business.
The monuments of consular, or Imperial, greatness were no longer revered, as the immortal glory of the capital;
they were only esteemed as an inexhaustible mine of materials, cheaper, and more convenient, than the distant quarry. Specious petitions were continually addressed to the easy magistrates of Rome, which stated the want of stones or bricks for some necessary service:
the fairest forms of architecture were rudely defaced for the sake of some paltry, or pretended, repairs;
and the degenerate Romans, who convened the spoil to their own emolument, demolished, with sacrilegious hands the labors of their ancestors.
Edward Gibbon, The History of the Decline and Fall of the Roman Empire, vol. 7 (Leipsick: Printed for Fleischer).

For anyone happening to be keeping score or totaling up the reasons … thought this excerpt interesting.