With the might of Chaos and Order eternally battling, a balance between them must also be fought for. Here, at the heart of the Nexus, is where that happens- drawing in the two primal forces, governing, generating a safe parallel energy... that is the awesome responsibility of Chronos.
Chronos is the presence who observes the power stuggle at play in Nexus and the dangerous shift of balance between the forces of Chaos and Order. Part of a machine known as the Oracle, Chronos is part biological and part machine, using his powers to regulate and control the primal energies that are diffused around the realms of Oblivion.
The complex machinery of The Oracle and other machinery within Nexus seems to outdate anything constructed in any of the other realms of Oblivion, with the Undine race possibly the nearest in technological advancement.
Nexus therefore is likely to have been created long before any of the other realms of Order or Chaos, possibly even by Chronos himself.