Although classical pieces can take whatever form a composer’s imagination dictates, many will stick to a length of somewhere from about 20 minutes to over an hour.
For ease of getting music performed composers often prefer to stick fairly closely to well-established groups of musicians, such as symphony orchestras and chamber ensembles of varying sizes and types.
Related: Music is far from just a man's world
Sometimes, however, all that simply flies out the window. Inspiration seizes and burns white hot and composers simply have to turn the rules and suggestions to ashes while producing music of truly epic length and scale.
Here’s a few much-loved and in some cases notorious marathons and mammoths from the world of classical:
Wagner - The Ring Cycle. A massive series of four operas lasting 15 hours telling of the downfall of the gods and destruction of a corrupt world. Don’t be put off: The Ride of the Valkyries is just the best-known example of Wagner’s brilliant orchestral writing.
Havergal Brian - Symphony No. 1 (The Gothic). This is officially the longest symphony ever penned. Over an hour and 45 minutes in six sections with a massive ensemble, choirs and brass bands involved.
Messiaen - Vingt Regards sur l’Enfant Jesus. An astonishing two-hour solo piano work in 20 sections exploring Christ and faith. The music ranges from the most delicate passages of contemplation to astoundingly complex and violent depictions of creation.
Feldman - String Quartet No.2. At six hours this is the most extreme example of Feldman’s late enthusiasm for very, very long and slow-moving pieces of music. If you can surrender yourself to this it has an extraordinary hypnotism and intensity.
Stockhausen - Licht. An opera for each day of the week telling of the world’s protection by an Earth mother and archangel against the devil. A theatrical strike, a war on stage, dazzling instrumentals, electronics - it’s all in here.