Thursday’s verdict will be a reminder of the scale of the killings – some 100,000 people died in Bosnia alone, with other victims in Croatia and Kosovo – and of the glacial pace at which justice has arrived.
I have a question regarding the usage of the preposition "at" before "which justice". I pressume that the author wants to say it lasted very long time before justice has realized. But I do not understand why "glacial pace at which" is used. Glacial pace is something like extremely slow speed so I would use "glacial pace by which justice has arrived". In the original sentence it is suggested that glacial pace is some kind of a place. Can you explain to me what's wrong with my consideration?