nearby town of Trà Kiệu which may be the site of the historical Cham city of Simhapura. Many architectural ornaments from this style survive and are displayed in the Museum of Cham Sculpture. A transitional style of the early 11th century to the middle of the 12th century is exhibited in Mỹ Sơn E4, F2, and the K group of sites. The style of Bình Định that prevailed in Cham architecture from the end of the 11th century, when the center of the Cham polity was displaced southward from the area around My Son to Vijaya in Bình Định Province, to the start of the 14th is represented by Mỹ Sơn B1 and groups G and H. Building techniques Most of the temples at Mỹ Sơn were made of red brick, and only one (the temple labelled "B1") was made of stone. Even the decorative carvings on the Cham temples were cut directly onto the bricks themselves, rather than onto sandstone slabs inserted into brick walls as is observable for example in the 9th century Cambodian temple of Bakong. To this day, the construction techniques used by the Cham builders are not completely understood. Issues that have not been completely resolved include issues about the firing of the bricks, the mortar between the bricks, and decorative carvings found on the bricks. At what point in the building process were the bricks hardened by fire? Were the bricks hardened first, and then arranged in order to build the structures, or were the structures built out of partially hardened bricks, after which the entire structures were heated by fire to finish the hardening of the bricks? The hypothesis that the entire structures were reheated following assembly is supported by evidence that the mortar between the bricks was at some point subjected to high temperatures. The contrary hypothesis is supported by the observation that the structures bear no signs of scarring from large intense fires such as would be needed in order to reheat them as whole. How were the bricks stuck together? One hypothesis is that the builders at Mỹ Sơn developed a way to glue bricks together using tree resin native to central Vietnam. Another hypothesis is that the builders used a sticky mortar made from the same clay as the bricks themselves. The latter hypothesis is supported by chemical tests that have found no trace of any organic substance between