Question: Montfichet's Tower was a Norman fortress on Ludgate Hill, in the historic centre and central business district of which city? 
Sentence (from "Montfichet's Tower"): Montfichet's Tower (also known as Montfichet's Castle and/or spelt Mountfitchet's or Mountfiquit's) was a Norman fortress on Ludgate Hill in London, between where St Paul's Cathedral and City Thameslink railway station now stand.
Relevant evidence: Yes