"Ahu" are stone platforms. Varying greatly in layout, many were reworked during or after the "huri mo'ai" or "statue-toppling" era; many became ossuaries, one was dynamited open, and Ahu Tongariki was swept inland by a tsunami. Of the 313 known ahu, 125 carried moai—usually just one, probably because of the shortness of the moai period and transportation difficulties. Ahu Tongariki, from Rano Raraku, had the most and tallest moai, 15 in total. Other notable ahu with moai are Ahu Akivi, restored in 1960 by William Mulloy, Nau Nau at Anakena and Tahai. Some moai may have been made from wood and were lost.