racks and deterioration. Van Erp used concrete from which alkali salts and calcium hydroxide leached and were transported into the rest of the construction. This caused some problems, so that a further thorough renovation was urgently needed.
Small restorations have been performed since then, but not sufficient for complete protection. In the late 1960s, the Indonesian government had requested from the international community a major renovation to protect the monument. In 1973, a master plan to restore Borobudur was created. The Indonesian government and UNESCO then undertook the complete overhaul of the monument in a big restoration project between 1975 and 1982. The foundation was stabilized and all 1,460 panels were cleaned. The restoration involved the dismantling of the five square platforms and improved the drainage by embedding water channels into the monument. Both impermeable and filter layers were added. This colossal project involved around 600 people to restore the monument and cost a total of US$ 6,901,243. After the renovation was finished, UNESCO listed Borobudur as a World Heritage Site in 1991. It is listed under Cultural criteria (i) "to represent a masterpiece of human creative genius", (ii) "to exhibit an important interchange of human values, over a span of time or within a cultural area of the world, on developments in architecture or technology, monumental arts, town-planning or landscape design", and (vi) "to be directly or tangibly associated with events or living traditions, with ideas, or with beliefs, with artistic and literary works of outstanding universal significance".
Contemporary events
Following the major 1973 renovation funded by UNESCO, Borobudur is once again used as a place of worship and pilgrimage. Once a year, during the full moon in May or June, Buddhists in Indonesia observe Vesak (Indonesian: Waisak) day commemorating the birth, death, and the time when Siddh?rtha Gautama attained the highest
