Which one was older, Artemis or Apollo?

Question

On the island of Delos, Leto had twins, Apollo and Artemis.

But usually, twins have a time in between before they are born. Not sure if this is the same in mythology.

So which was older?

Answer 1

Most accounts that make the distinction agree that it was Artemis who was born first.

From Pseudo-Apollodorus, Bibliotheca 1. 21:

She [Leto] finally reached Delos and gave birth to Artemis, who thereupon helped her deliver Apollon. Artemis became a practised huntress and remained a virgin.

From Callimachus, Hymn 3 to Artemis 22:

Even in the hour when I [Artemis] was born the Moirai (Fates) ordained that I should be their helper [women in childbirth], forasmuch as my mother suffered no pain either when she gave me birth or when she carried me win her womb, but without travail put me from her body.

^{Both quotes from Theoi.}

Note that some accounts imply that there was a separation between the birth of the twins (see e.g. the references in Woman's Power, Man's Game: Essays on Classical Antiquity in Honor of Joy K. King), but this is not explicitly stated anywhere, as far as I know.