What can this mean? I have several thoughts:
- Apollo Thanatos, who brings death with his deadly arrows, killer of youths, defender of the city, striker from afar - Apollo delivers death and, therefore, he is at Hades entrance;
- On the other hand, Apollo Paian, who delivers health and keeps death away also seems eligible to have a temple at Hades' entrance, for he would stand there and decide if one would die or live, which also relates to His aspect of prophet and his epithet Moiragetes;
- Apollo Alexikalos, who purifies, also has a right to stand on Hades' entrance to rid one of all lies and miasma so that our soul would be pure again and either be judged or enter Hades or reincarnate, depending on one's believes;
- Apollo Isodetes, who binds all equal could also be a judge on Hades to distribute souls according to some divine criteria;
- Apollo Phoibos as patron of Philosophy, according to Plato, could be the final step upon soul ascension: in short, Philosophy is the work of the soul and philosophers upon dying would rise and join the Gods, while those who didn't work out the soul would fall again and reincarnate - this according to Plato theories. Therefore, if this "temple at Hades' entrance" is only found in Plato it can mean this;
- Apollo is also called Dionusodotes, the one who gives Dionysus, and this God in undoubtedly connected with death and life beyond death;
- Finnally, Asklepios, Apollon's son, once resurrected a man, which could theoretically not be done for, according to Zeus in the myth, it is against the Divine Order. Because of this Zeus punished him, however Apollon revenged his son by killing the cyclops, which shows how he supported his son - in my opinion Divine Order cannot be broken unless the God who watches over it allows it to happen. Apollo clearly was pro-resurrection in this case and therefore could well be the God who allowed Asklepios to resurrect a man.