Sir Christopher Wren was the architect entrusted with designing a stone replacement for the wooden barrier that was lost in the Great Fire of 1666. It was later dismantled and removed from the city in 1878 (given away, actually, to Sir Henry Meux, who reassembled it in his private park near Waltham Cross). Curiously, it was purchased by the Temple Bar Trust from the Meux Trust for £1 in 1984. In 2003 Temple Bar was carefully dismantled yet again and transported back to London on 500 pallets and re-erected as an entrance to Paternoster Square just to the north of St Paul's Cathedral. It opened to the public the following year.
Note: When the sovereign left the City of Westminster and headed for St. Paul's Cathedral in the City of London, it was necessary to stop the procession and ask permission of the Lord Mayor to enter London proper.