Antonio Valera lays out this narrative in a way that is a little more understandable than I've seen previously. The period in question for simplicity's sake nominally begins sometime at the end of the Middle Neolithic in which a great acceleration in economic complexity, social inequality, and monumentalism begin in the region.
This process peaks in the Chalcolithic with some of Europe's first stone fortresses and intense, long-distance trade, but then it is rather abruptly followed by a strange period of monumental silence. Since this paper is still not yet available, I'll condense to what I think is the most important take-aways below.
|Outeiro Alto Sinuous Ditched Enclosure|
As the ditched enclosures become larger they are at some point joined by walled enclosures [here1]
[here2] in the 3rd millennium. These stone forts are perched on high terrain and have every strategic indication of fortification, both having defensive features and favorable terrain but also a considerable amount of projection on the landscape. (The builders of these forts were not Beakers or not yet Beakers.) (Again me: another interesting relationship between the walled enclosures and the large, ditched enclosures of Alentejo, appears to be the fact that copper used in the large forts like Zambujal appear to have come from the Alentejo region) ((more wild ass speculation))
Things begin changing around the time in which Bell Beaker culture emerges, although it is not clear that it is Bell Beaker that is the reason for these changes. (It's possible societal collapse preceded the Beaker phenomenon) Up to this point as Valera describes, much of the structures in the landscape are positive in nature... large monumental structures for burial, for living, for defense, all large, all imposing on the landscape. You may expect this type of behavior from people continually establishing their entitlement to the land in which they live.
They had many iconographic displays of people, creatures and plants, sometimes in a more schematic format, but other times more naturalistic. However this society, as understood, comes to an end. As the monuments fall into disrepair, no others will be built. The positive tombs and forts in the landscape are replaced by negative structures.. pit graves, cairns, hypogea. Sometimes a megalith is re-used as a grave for a Beaker person, and even less so is a fort or ditched enclosure maintained for a while, but nothing new is built, and for the most part these great fortresses collapse. Hillbilly Bell Beakers build huts on the ruins and throw their beer cans in the front yard. (your's truly)
It is during this period that Valera describes as being almost iconoclastic, rejecting the naturalism and iconography of the megalithic-chalcolithic tradition for a more subtle geometric art, but a continued taste for loud, gaudy materialism.
Why all the ditches?
The purpose of a desert kite is so simple it's stupid. It could be ditches and cross ditches just keep retarded goats from climbing fences. Ditches are still to this day one of the simplest and most effective defensive obstacles. But if these were the case then why did it stop?
"Social change in the late 3rd millennium BC in Portugal: the twilight of enclosures" Valera, Antonio (published 2015) "2200 BC - A climatic breakdown as a cause for the collapse of the old world?" Landesamt fur Denkmalpflege und Archaeologie Sachsen-Anhalt: Mitteldeutscher Archaologentag.