1970s, it was determined that the 5.11 climb was much harder than 5.10, leaving many climbs of varying difficulty bunched up at 5.10. To solve this, the scale has been further subdivided for 5.10 and above climbs with suffixes from "a" to "d". , only one climb is considered to have a difficulty of 5.15d: Silence, first climbed by Adam Ondra on September 3, 2017. Other systems There are other systems used throughout the world. They are covered in the article about Grade (climbing). See also Aid climbing Ice climbing References Climbing Rating systems Sierra Club