Hardest Piano Song

On the piano the technique endurance and rhythmic harmonic complexity of these pieces are what earn them their top spots.
Hardest piano song. La campanella which translates as little bell comes from a larger work the grandes études de paganini and is famous for being one of the most difficult pieces ever written for piano. Liszt la campanella. However some would argue that a somewhat simpler piece can be more difficult to play with. Writing an article on the most difficult piano piece presents its own difficulties.
Which periods of music should one consider and should the article consider only technical challenges or other subtler musical difficulties. If we could fill this list with liszt pun intended we absolutely would. Everybody has a different perspective on what makes a song difficult. Most difficult piano pieces hardest piano pieces.
These are purely for show and not tutorials.