As the Panama Canal has historically been such a vital passageway in the development of global trade, the size of the original canal locks have given root to a ship size-specification that was long the standard for global shipping: the Panamax.
The Panamax (see diagram) is defined by having a beam (the width of a vessel) of 32m, allowing it to just squeeze into the 33.5m Panamanian locks. This size of ship was crafted in the 1980s after the mass development of the TEU (twenty-foot equivalent unit) container in the previous decade; the combined factors of a boom in international trade and a nascent globalised capitalism rendered the containership an ideal form of cargo movement.
Therefore, the size specification for a ship regarding its capacity is measured by the amount of TEU it can hold, and by the mid-80s, the Panamax could haul up to 4,500. However with trade branching all over the globe, there was a desire to get even bigger yet.
Creating the post-Panamax was a risk. Draft (how deep a ship extends underneath the water) was an issue, as was capacity at ports; and also, whether the infrastructures at ports could handle the post-Panamax loads and the fact that shippers would have to redefine global trade routes. However, yet again, demand from a global market rendered the post-Panamax a reality, and by the millennium ships of up to 8,000 TEU had been established on service routes around the globe.