The basic unit of the ancient Hawaiian land division system was the "ahupua'a", a self-sustaining agricultural district. The places where a road crossed the border of an "ahupua'a" were marked with distinctive altars, known as "ahu" or (stone) piles. These altars served not only as boundary markers but also as sites for the performance of religious rituals related to land taxation. C. J. Lyons, an early surveyor of Hawaii, recorded that "this altar at the annual progress of the akua makahiki (year god) was deposited the tax paid by the land whose boundary it marked, and also an image of a hog, "puaa", carved out of kukui wood and stained with red ochre. … [From this came the name, "ahupuaa"“. Naturally occurring landscape features were also used as points of reference for district borders.