Abstract: The history of the canal systems in Kilimanjaro Region, the largest cluster of “hill furrows” in eastern Africa, is central to the history of water in the region. The main objective of this article is to analyse the development of these systems at Mt. Kilimanjaro. Two hypotheses about changes in water use in the densely-populated districts where these canal systems are found are used to guide policy and interventions in traditional irrigation. According to the first, the hill-furrow system is in decline, as schemes become redundant with development and transition to piped water supply. According to the second, conflicting hypothesis, the post-independence era has seen an increase in the hill-furrow technology driven by population growth. Basic questions of how and when the systems were initiated and subsequently expanded remain to be answered. Oral traditions suggest that the technology was established several hundred years ago, while eye-witness accounts from 1848 onwards show that the technology was widespread across the southern slopes of Mt Kilimanjaro and beyond. Data from studies documenting the extent of the irrigation infrastructure during the 20th century show moderate changes in the number of schemes. A substantial canal infrastructure was developed prior to the population expansion it has been ascribed to. This supports a third, alternative hypothesis, that irrigation infrastructure was fully developed in many highland areas by the early 20th century, and that 20th century changes can be seen as a restructuring of irrigation, under the influence of several factors, where a decline in the densely-settled highland areas has been offset partly by increase in irrigation in new areas and partly by increase in scale.