All that said, there are considerable areas of scholarly agreement and it is the aim of this section to set these out. It is also worth saying that the volume and quality of evidence available has improved markedly, particularly since the 1980s. The study of Byzantine coins, the excavation of Byzantine sites, including underwater archaeology, the study of pottery types and the publication of texts and associated linguistic studies have all made great advances. But it is also important to recognise that Byzantium is not a well-documented society. Late antique Egypt provides an exception, but it was lost to the Muslims by the mid-seventh century. The rich materials from the Cairo Genizah will be referred to later, and the vivid picture they give of Mediterranean commerce in the eleventh and twelfth centuries is a reminder of what we are missing. The masses of largely monastic documentation that underpin so much of traditional economic history in the west do not exist for the Byzantine world. After 1204, Latin documentation will make a significant difference, not only by reason of its quantity, but because we are talking of new types of evidence: commercial documents preserved in secular archives. This material begins to appear before 1204, but its real contribution comes later (see below, pp. 843–4). This would not matter so much if the lack of documents were offset more fully by archaeology. Recent advances in our understanding of the economy of western Europe during this period have come as much from this direction as any other. Pottery studies, for example, have shown that even remote villages were involved in networks of exchange. Pollen studies have shown both the early date and ultimately the permanent effects of medieval agricultural expansion. Similar work has been done for the Byzantine world, but it lags behind what has been achieved in western Europe.2 Even so, there are considerable areas of scholarly agreement and the story of Byzantine economic history over the last thirty years has been one of solid achievement.