Board Thread:Lore Discussion/@comment-6707115-20130619015913/@comment-6707115-20130621182835

Maybe the covenant was only what Akatosh had told Alessia, "that so long as the dragonfires are lit and our joined blood holds this amulet, then I shall endevor to keep shut the jaws of Oblivion". I also believe that the original intent of that covenant was to deny the elves (the Aylieds specifically) their infinite armies of daedra, so perhaps it only counts for Oblivion gates capable of transporting armies. Thus explianing why Sheogorath's simple door to oblivion was able to stay open after Martin's sacrifice.