Gregory the Great — as excerpted in the Catena Aurea on Luke 19:41-44

“This too which is added, namely, They shall not leave in thee one stone upon another, is now witnessed in the altered situation of the same city, which is now built in that place where Christ was crucified without the gate, whereas the former Jerusalem, as it is called, was rooted up from the very foundation. And the crime for which this punishment of overthrow was inflicted is added, Because thou knewest not the time of thy visitation.”