What happened to the Mediterranean harbour installations after the Imperial period? How can we interpret that qualitative and, at least in part, quantitative, collapse which appears from a superficial analysis of the archaeological remains? Does the problem of the lack of visibility of the evidence for late antique harbour contexts – caused by both natural and anthropic phenomenona effecting their disappearance whether due to their lesser monumentaly, hence less striking construction techniques – exist? Is it possible, in the end, that the knowledge of harbour engineering, developed after the Augustan period, due especially to the use of concrete with pozzolana, was lost or no longer used? Having provided an overview of the results of recent investigations that have focused on a number of Mediterranean harbours built in the Late Antique period and the Late Antique phases of harbour contexts founded in the imperial period, this article wishes to go beyond the traditional approach, founded on the concept of the "decline" of the functionality and of the monumentality of the harbours, based often only on traditional sources. Taking into consideration obviously the deep technological and topographical differences of harbours in the two halves of the Mediterranean, and using, for comparison the insediative logic of harbours of the North European coastal landscape, we analyse the processes that occurred in the Mare Nostrum in a phenomenon marked by the physical remodeling of the harbours for reduced necessities, both of functional type and especially of ideological type. We intend thus to consider this shift as a sort of return to "normality" and the late antique period, here under special scrutiny, appears once again as a crucial moment where such landscapes are evident. In this period, indeed, we record opposite signs of behaviour, which range from the extreme of new harbour models closer to those of the ancient world to the return to a widespread, and almost total, use of the wood. However this recovery of the "normality" uses at least part of the now unnecessarily imperial installations and, in case of the foundation of new harbours, uses techniques and materials that are less monumental but no less functional than those of earlier times, at least with regard to their reduced needs. [Author]