Our guide took us on the extended tour today to see even more temples in the Siem Reap area. These temples are all a bit smaller and less well known than the ones we saw yesterday, so they were also less crowded.
Several were built by the same king who built the Bayon temple we saw yesterday with all of the faces. Bayon was built to honor both the Hindu and Buddhist faiths (he was Buddhist but his wife was Hindu), and these other ones were built to honor various ancestors (parents, grandparents, etc). You'll notice that a few of these temples used bricks in their construction rather than the usual sandstone. The large sandstone blocks had to be carried downstream from the mountains via rafts and elephants, but the bricks could be made with local materials. The bricks would have then been covered in plaster and carved similar to the others, but the plaster hasn't survived. There is ongoing restoration, so some of the carvings are clearer than others.
The last temple we visited is one of the oldest temples in the area, about 15 miles north of the rest of the temples. Banteay Srei was built in the 10th century, so it predates the other temples by 100-200 years. The carvings on this temple were deeper into the sandstone than the other temples, so despite being older, the carvings are still remarkably clear. Much less erosion here.
We asked our guide why so many temples were built in the same area, by different kings and over the course of a few centuries. The answer: water. We aren't right next to the main lake here, but apparently during the height of rainy season, the flooding comes pretty close. The underground water level is pretty shallow here, which means digging a well for drinking water or to irrigate the rice fields is very easy. Other parts of the region, not so much.
Most of these temples were built as Hindu temples (except as noted above, with one king building both Hindu and Buddhist temples together). There was apparently a lot of fighting between Hindu and Buddhist factions throughout the years, so one King outlawed Buddhism in an effort to bring peace to the region. He forced the removal of all Buddha images from some of these joint Hindu-Buddhist temples, so there are gaps in the carvings where you can tell Buddha used to sit in meditation. All of the temples later became Buddhist temples as Buddhism became the dominant religion here, several centuries later. The statues of the Hindu gods were removed, and Buddha statues installed instead.
Eventually, all of the temples (except Angkor Wat) were abandoned as the Khmer people retreated towards Phnom Penh to get further from the Thais in the 16th century. A small group of people continued to live at Angkor Wat, so it was/is continuously used as a Buddhist temple. The other temples were eventually taken over by the forest and not rediscovered until the early 1900s.
Restoration didn't begin in earnest until the 1970s and was often slow going during the Cambodian civil war. Once the war ended in the early 2000s, more tourists started arriving and international restoration efforts expanded. Our guide told us in 2009, they had 1 million visitors in a year, and by 2012, over 4 million. I don't know what they're up to now, but it's a lot. It's low season now, and it still seems very crowded to me. An Australian family in line with us at Angkor Wat had visited in 2002, and they said it was hugely different back then. Very few tourists, no restrictions on where they could go/climb, etc. It's much more regulated now - ticket checks at each temple, lots of guards all over the temples so you don't climb anywhere inappropriate, etc. Personally, I love the ruins part of these temples (sandstone blocks piled up where they've crumbled, trees growing over the stone, etc), so I hope they don't do the restoration too swiftly.
(My facts here are as I remember them from the tour guide explaining them, so I hope I got it mostly right. Major thanks to our private tour guide for two days of explanations and answering questions. If you visit here, I'd highly recommend booking a private guide/car. Not very expensive for Americans (though expensive by Cambodian standards where a restaurant meal costs $3), and the knowledge of the history, where to go in each temple, plentiful cold water, and air conditioning between temples is totally worth the expense. Lots of folks get a guidebook and tuktuk driver for the day (or bike themselves), but IMO, the licensed guide is worth every extra penny.)
