Wales manager Chris Coleman said his players "know what's at stake" as the country prepares for its biggest football match in almost 60 years.
They face Belgium knowing victory will clinch them a place in the semi-finals of Euro 2016.
Wales have not reached a major finals since they were beaten by Brazil in the last eight of the 1958 World Cup.
There will be about 20,000 Wales fans in Lille for the match, but with the city just 10 miles from the Belgian border, it has been estimated there will be up to 150,000 Belgium supporters making the trip.
This has led to concerns that many ticketless Welsh fans may not even be able to get into the Lille fan zone, which holds 30,000.
Belgium manager Marc Wilmots said his team will have home advantage, adding that it will be great to have the 12th man.