‘Water’ merits an entry as a keyword for three reasons. First, although we tend to think of homo sapiens as principally a terrestrial species, water in its various forms has always been a key medium and focus for human travel. Second, since water is a primary phenomenological and symbolic reference point for all that is not fixed, immobile and rigid, tropes of fluidity, porosity and other terminology derived from water and the earth's water systems occur frequently in scholarly and popular discourse on travel – providing a naturalizing imagery which can serve, some critics suggest, to occlude the political and socioeconomic contexts to historically specific patterns of movement (Pratt 2008 [1992], 241–42). Finally, across a broad range of academic fields, seas and oceans have recently emerged as principal units of enquiry rather than the more traditional nation states and continents. This epistemological reconfiguration – sometimes dubbed the ‘New Thalassology’ or ‘blue studies’ – reflects environmental and geopolitical concerns, and is especially driven by the recognition that a maritime or oceanic focus often highlights the skewed or partial perspectives, and nationalistic investments, inherent in traditionally focused historiography and cultural analysis (see Quilley 2000).

Water covers 70 per cent of the planet, is the principal constituent of our bodies and is essential to life. Yet when accumulated even in moderate quantities it creates environments profoundly hostile to a land-based mammal such as homo sapiens. This duality is echoed in other contraries and paradoxes that commonly pertain to water. For example, large bodies – such as rivers, lakes and especially seas – frequently mark the division and border between territories, nations and continents. Aqueous environments are thus often liminal zones, epitomizing flux and instability, and therefore regarded as ‘other’ to the norms of life on dry, solid land. Yet while cultures have often emphasized the profound alterity of aqueous environments, water is also a crucial medium of connection as well as separation. Notwithstanding its dangers, travel by water has often been easier than travel by land, given poor roads and the impenetrability of many interior regions. This was (and remains) especially the case when heavy loads require transportation. For this reason, boats, rafts and other vessels were being constructed even in very early prehistoric times.