Migration is rarely out of the news, and the movement of people has become one of the most politically charged issues of the day. At the time of writing, Pope Francis is embroiled in a spat with presidential hopeful Donald Trump over the issue of Mexican migration to the USA, attempts to restrict the free movement of European citizens underlie much of the discussion of the forthcoming UK referendum and refugees continue to flee war-torn Syria. In such a context, the symbolism of Neil MacGregor's choice for his final curatorial acquisition for the British Museum is potent: a cross fashioned from wood salvaged from a migrant ship wrecked on the island of Lampedusa.

With over half of the world's population living in cities, urbanism is one of the defining characteristics of the contemporary age. In the past, by contrast, most people lived scattered in villages and rural settlements. Yet pre-industrial cities still exerted a disproportionate influence on society, economy and culture. In Cities that shaped the ancient world, John Julius Norwich collects 40 of the most influential. Taking inspiration from this urban super league, this instalment of New Book Chronicle tackles a selection of new volumes, each concerned with one of the cities identified by Norwich, taking us 5000 years and 13 000 km from Ur to Tikal. Each book also presents a different publication format, offering the opportunity to think not only about the individual cities, but also how we write about them.

For this issue of New Book Chronicle, we don lifejackets and head out on, and under, the high seas to review recent volumes on aspects of maritime and underwater archaeology. Along the way are tales of pirates and the odd Sherman tank, but we set sail with Site formation processes of submerged shipwrecks, edited by Matthew Keith. The Introduction, by Oxley and Keith, outlines the development of site formation theory in maritime archaeology, and flags the foundational work of Keith Muckelroy, as summarised through his flow diagram of the sequence of cultural and environmental processes at work between a wrecking event and archaeological investigation. This model features strongly not only in the following chapters, but in every one of the volumes considered below.