Six works by Chinese artist and dissident Ai Weiwei, who is currently confined to Beijing, went on sale at a major contemporary art fair that got under way Wednesday in Spain. The pieces include a dark blue porcelain pillar that is around three metres (nine feet) tall with an asking price of 150,000 euros ($200,000) and a green and black porcelain watermelon for 50,000 euros. They were brought to the ARCO art fair by Madrid gallery Ivorypress which selected Ai -- whose activism has made him a thorn in the side of China\'s communist authorities -- as its \"featured artist\" at the five-day event. \"He was chosen because he is relevant at the international level and to give him greater visibility at this time,\" said a spokeswoman for the gallery, which was founded by Elena Foster, wife of acclaimed British architect Norman Foster. Ai disappeared into custody for 81 days last year as police rounded up dissidents and lawyers amid online calls for Arab-style protests in China. The value of his sculptures, photographs and installations has shot up since his detention thrust him into the global spotlight, and in October Britain\'s influential Art Review magazine named him the most powerful figure in the art world. The bearded, burly 54-year-old artist -- whose sunflower seeds installation was exhibited at London\'s Tate Modern last year -- denies tax evasion charges and says the case is a politically motivated attempt to silence him. He was released in June but is prohibited from leaving Beijing. Ai has angered Chinese authorities with his investigation into the collapse of schools in the 2008 Sichuan earthquake and into a 2010 fire at a Shanghai high-rise that killed dozens. A total of 215 art galleries from 29 countries are taking part in ARCO, which displays works by roughly 3,000 artists.