Construction beginning/end
During the first civilisations that dawned on Eden's Plateau, cross continental naval travel was almost impossible for the Antederelictians. But eventually, using the eldritch magics they gained from the many Obelisks they found, they created massive Land Bridges to traverse the ends of the Ocean. The reason for this was because they sought The Black Towers, believed to be the source of all magic on what is now the Forbidden Continent.
Overtime most of these bridges were converted into habitable lands which took over a thousand years.