In this study, an attempt is first made to describe the activity of transshipment, while examining the development and operation of modern mega transshipment hubs, as well as all the elements that contributed to their emergence and development. Next, a review of contemporary scientific literature is followed to determine the position of these hubs today within the global supply chains and how they contribute to shaping their competitiveness. The following section examines the development of this economic activity in the Mediterranean Sea region and presents the criteria that have formed in the past and which continue to affect the development of transshipment in that region today. Finally, a comparative analysis of the largest hubs in the Piraeus follows, according to their movement data collected during the years 2007 to 2015, while identifying the factors that contributed to their emergence.