Ancient civilizations have passed down to us a vast range of monumental structures. Monumentality is a complex phenomenon that we address here as ‘XXL’. It encompasses a large range of different aspects, such as sophisticated technical and logistical skills and the vast economic resources required. This contribution takes a closer look at the special interdependence of space and knowledge represented by such XXL projects. We develop a set of objective criteria for determining whether an object qualifies as ‘XXL’, in order to permit a broadly framed study comparing manifestations of the XXL phenomenon in different cultures and describing the functional and conceptional role of the phenomenon in antiquity. Finally, we illustrate how these criteria are being applied in the study of large construction projects in ancient civilisations through six case studies.