From the 1820s to the 1850s, the British Indian state undertook its final major phase of expansion to assume the approximate geographical extent it retained until its demise in 1947. It confronted at its north-eastern and north-western outskirts seemingly intractable mountains, deserts, and jungles inhabited by apparently stateless ‘tribal’ peoples. In its various attempts to comprehend and deal with these human and material complexities, the colonial state undertook projects of spatial engagement that were often confused and ineffective. Efforts to produce borders and frontier areas to mark the limits of administered British India were rarely authoritative and were reworked by colonial officials and local inhabitants alike. Bringing together diverse examples of bordering and territory-making from peripheral regions of South Asia that are usually treated separately lays bare the limits of the colonial state’s power and its ambivalent attitude towards spatial forms and technologies that are conventionally taken to be key foundations of modern states. These cases also intervene in the burgeoning political geography literature on boundary-making, suggesting that borders and the territories they delimit are not stable objects but complex and fragmented entities, performed and contested by dispersed agencies and therefore prone to endless fluctuation.