Bagan became a central powerbase of the mid 9th century. King Anawratha, who unified Burma under Theravada Buddhism. It is estimated that, at one time, more than 13,000 temples and stupas once stood on this 42-sq km plain in central Myanmar, and Marco Polo once described Bagan as a "gilded city alive with tinkling bells and the swishing sounds of monks' robes". Approximately 2,200 remain today, in various states of disrepair. Some are large and well maintained, such as the Ananda Pahto, others are small tumbledown relics in the middle of overgrown grass. All, however, are considered active sacred sites, so when visiting even the least conspicious, be sure to behave in a respectful manner.Bagan's golden age ended in 1287 when the Kingdom and its capital city was invaded and sacked by the Mongols. Its population was reduced to a village that remained amongst the ruins of the once larger city. In 1998, this village and its inhabitants were forcibly relocated a few kilometers to the south of Bagan, forming "New Bagan." Today the city is abandoned, with the exception of a few hotels and religious centers.Despite of his size and importance Bagan is not listed as UNESCO World Heritage List|world heritage site, because many of the temples are rebuild in a way the UNESCO calls ''un-historic''. http://wikitravel.org/en/Bagan