In 1863 the first underground passenger railway in the world opened in London. It ran for just under seven kilometers and allowed people to avoid terrible ¡¡¡¡1.crowds¡¡¡¡(crowd) on the roads above as they travelled to and ¡¡¡¡2.from¡¡¡¡ work. It took three years to complete and was built using an interesting method. This included digging up the road, ¡¡¡¡3.laying¡¡¡¡(lay) the track and then building a strong roof over ¡¡¡¡4.the¡¡¡¡ top. When all those had been done, the road surface was replaced.