In the Ayodhya Kanda of the Ramayana, Kaikeyii's evil servant Manthara convinces Kaikeyii to exile Rama and make her son Bharata as king. Manthara reminds Kaikeyii that she had received two boons from Dasharatha, because she had saved Dasharatha's life in a war:
O Queen! Once upon a time, when there was a battle between celestials and demons, your husband Dasaratha went along with you and other holy kings to help Indra in battle, to a famous city called Vaijayanta in which the demon Timidhvaja lived in a southern direction in the forest of Dandaka. That great demon famously called shambara, who had several magic effects, defeated all the celestials and conferred battle upon Devendra. In that great battle, demons approached and forcefully killed men who were injured by arrows and also those who were sleeping at night.
Then, king Dasaratha fought a great battle there. With their weapons, demons made into pieces the long armed Dasaratha. O Queen! You saved the life of your unconscious husband by taking him away from the battle field. There also, you again saved him, when beaten by demons with their weapons. O Kaikeyi with auspicious appearance! Getting delighted, he gave two boons to you. Then, you said, "I shall ask you whenever I require them". He then agreed to it.
My question isn't about Kaikieyii's infamous two boons, but rather about the war that Dasharatha was fighting in. My question is, who is this Asura (demon) called Timidhwaja or Shambara whom Dasharatha and "other holy kings" helped Indra to fight?
There is one demon by the name of Shambara who was famously defeated by Indra to help the king Divodasa, as described in numerous hymns in the Rig Veda including this one:
In the wild joy of Soma I demolished Śambara's forts, ninety-and-nine, together;
And, utterly, the hundredth habitation, when helping Divodāsa Atithigva.
(Who the I is in this hymn is actually a complicated issue that I may discuss in a future question, but suffice it to say that it's about the deeds of Indra even though the "I" may not be Indra.) So is this Shambara who had a hundred forts the same Shambara that Dasharatha helped fight? Is this city of Vaijayanta in the Dandaka forest the hundredth fort of Shambara, which Indra "utterly demolished"? That would explain why Rama didn't encounter any such city when he was exiled to the Dandaka forest many years later.
On a side note, the Kamba Ramayana claims that Jatayu the bird fought alongside Dasharatha in the battle against Shambara, as I discuss in this question.