The record of human life in the Triangle becomes clearer when the first surviving signs of human habitation appear. All over the region, and in areas surrounding it, stone tools are important guides. Archaeologists think that these tools were used in many ways: for cutting, cleaving, drilling, digging, smashing bones, scraping, sewing, hewing wood, carving bamboo and perhaps making stone-tipped spears or harpoons.

The oldest dated traces of human habitation have so far been found in the Indo-Burma Arc. Here a large cave has yielded stone and bone tools, ash and many bones of small game animals, as well as a partial human skeleton. The people who used the cave are thought to have been hunter-gatherers who lived here in the fifth millennium BCE (Plate 3.1).

It has proven extremely difficult to date archaeological finds in this region, partly because, until recently, sophisticated fieldwork was rare. Dating is becoming easier because problem-oriented, methodologically rigorous and multidisciplinary archaeological studies are now emerging. According to archaeologist Manjil Hazarika, there are specific local obstacles. In the flooded river valleys, annual deposits of sediments cover older deposits, and thick vegetation in the mountains makes it difficult to prospect for surface objects. Extreme monsoon rainfall hampers fieldwork, and so do various regional insurgencies. Mountain cultivation disturbs the topsoil and likely destroys archaeological contexts. Finally, high groundwater levels make it difficult to establish stratigraphic sequences, and the year-round humid climate leads to rapid decomposition of materials other than stone. It is likely that humans made tools from all kinds of material, notably wood, bamboo, bone and plant fibre (for example, to make animal snares). In river valleys and deltas stone was rare; but for this early period, only stone, fossil wood and bone tools have survived – or, at least, have so far been recovered. Material remains from these early times point towards affinities with Southeast Asia rather than with the Indian peninsula.

This era is usually referred to as the Palaeolithic (or Old Stone Age) and the next, when crop cultivation develops, as the Neolithic – but these terms are problematic. They are derived from European archaeological narratives and should be treated with circumspection because they may not be directly applicable to local conditions. Here early stages of human development may have unfolded differently. Current understandings are that here ‘Palaeolithic’ groups co-occurred with ‘Neolithic’ groups for a very long time, probably millennia.