The UIAA grading system is mostly used for short rock routes in Western Germany, Austria and Switzerland and most countries in Eastern Europe. On long routes it is often used in the Alps and Himalaya. Using Roman numerals, it was originally intended to run from I (easiest) to X (hardest), but as with all other grading systems, improvements to climbing standards have led to the system being open-ended. An optional + or – may be used to further differentiate difficulty. As of 2018, the hardest climbs are XII.