I'm particularly interested to know when it became common for hell to be thought of a place "under" the earth.
In addition, I'd love any recommendations for books that might cover this topic in more depth.
A brief history of Hell
Within the Bible four words are used that could conceivably link to the notion of ‘Hell’. I say this, because common and contemporary notions of Hell do not always match conceptualisation and word usage within the Biblical documents, and the word ‘Hell’ is an English word that needs explanation anyway. So let me begin by giving you a brief handy guide to what ‘Hell’ usually refers to within Christian theology.
Christian theology is marked by a belief that Jesus will return again, and this event will act as a catalyst for a day of judgment. Depending upon certain beliefs/denominations/trajectories, how that plays out differs, but that it plays out is a fairly common/core belief. Believers at that point will experience a resurrection and some kind of eternal existence with God in a very nice place, non-believers will experience a resurrection and some kind of (eternal) existence in a not-very-nice-place. These two places are often called Heaven and Hell.
However, prior to Jesus’ second coming, most majority theologies teach that believers are already experiencing some kind of nice-place with Jesus, and this is also often called ‘Heaven’, while non-believers are already experiencing some kind of not-nice-place, and this is also often called ‘Hell’, and there is plenty of debate about whether or not, and how, Heaven 1.0 and Heaven 2.0 are related or not, and likewise Hell v1.0 and Hell v2.0. That is leaving aside opinions about annihilationism and universalism.
Okay, on to the Bible…
In the OT we find the word Sheol used as a fairly generic word for “the place of the dead”. In the KJV this is often translated as Hell, but that practice has largely been abandoned by translators. Sheol seems to be depicted as a place under the ground or like a pit (see, for example, Amos 9:2 If they dig into Sheol, / from there shall my hand take them; /if they climb up to heaven, / from there I will bring them down). However this in itself does not necessarily mean they thought of Sheol as a distinct place under the earth. I am inclined to understand most usages as metonymic, i.e. the dead go in the ground, so ‘in the ground’ is a handy way to refer to ‘where the dead are’.
Sheol seems to be a place that involves spiritual separation or opposition to God (for example Isa 38:18), but not the absence of God entirely (Ps 139:8). Sheol seems like a ‘hazy place’ in the OT, and expectations about it are hazy as well. Particularly unclear is the question of whether ‘the righteous’ end up there or not. Some texts seem to suggest a hope of not ending up in Sheol (Psa 16:10-11, 23:6, 49:15).
In the NT there are three words to consider, Hades, Gehenna, Tartarus. All have extra-biblical assocations that shape/contribute to their meaning. Hades is used in the Greek translation of the OT to translate Sheol, as well as in the NT to indicate ‘the place of the dead’. In Greek literature it is used to refer to both ‘the place of the dead’ and the Greek god responsible for overseeing it. The former meaning seems to be uppermost in NT usage. So sometimes it is relatively neutral, i.e. ‘where the dead are’, sometimes it has associations of torment or punishment, for example in Matthew 11:23 or in the parable in Luke 16:23.
Gehenna derives from a Hebrew place name Gehinnom, meaning the ‘valley of Hinnom’, which was a valley south of Jerusalem used for worship of gods-other-than-YHWH, and latter as a rubbish dump and place to dump animal and criminals’ bodies. Perhaps because of continual fires there, the word came to be used for the fire of judgment of the wicked. This happens at least within the intertestamental Jewish writings (i.e. Jewish writings written before the NT but after the close of the OT canon, so circa 400 BC – 55 AD). So, for that reason, Gehenna is used as a depiction of final judgment in the NT (Hell 2.0).
The last word, Tartarus, appears only in 2 Peter 2:4, where it refers to a place of punishment for fallen angels. The word in extra-biblical Greek writings and mythology is a place below Hades, where Titans and other threats to the Olympian gods are punished/kept. That may be why it is used in 2 Peter, as distinct from Hades.
So, coming back to your question, both Sheol and Hades have associations of being in ‘the underworld’, even though they don’t necessarily pick up all the connotations that, Hades for example, has in extra-biblical literature.
Looking at church history, most discussion is around issues of punishment, eternality, justice, rather than ‘location’ per se. To the extent that a lot of the cultures that Christianity spread into operated with a ‘heaven above’ ‘bad stuff below’ conception, at the very least metaphorically it was convenient to use those categories to speak about Heaven and Hell. So I’m not sure I would make any specific argument about when this idea ‘emerged’ except to say that it was ‘already there’ in the biblical literature and continued to be imagined that way, even when the specific idea of location was not under discussion.
Oops, used up my lunch break. Back soon with some reading suggestions.
Edit:
You might find the following helpful reading
Johnston, P. Shades of Sheol: Death and Afterlife in teh Old Testament 2002.
Tromp, N. Primitive Conceptions of Death and he Netherworld in the Old Testament 1969.
Longenecker, R. (ed) Life in the Face of Death 1998, esp pages 51-79
Any 'Dictionary' of Bible or also Classical Mythology will also have some entries getting you into the field and should provide some secondary literature to follow up.
hi! hopefully someone can drop by with some specific answers & recommendations, but meanwhile there have been several very interesting threads on Hell that may be helpful
How have Christian ideas about hell changed over time?
What were the christian beliefs on heaven and hell before Dante's The Divine Comedy?
Where does the idea of hell come from?
Where did the idea of Satan ruling over Hell in Christian beliefs come from?
Since no one's answered this directly yet, I might just refer you to this question which was asked recently: Where did the idea of Satan ruling over Hell in Christian beliefs come from?.
In this comment, I touched on some issues directly relevant to when it first entered into Jewish thought. But to elaborate a bit more: early Judaism has almost certainly always had a concept of an underworld afterlife realm (Sheol). This would be in keeping with standard ancient Near Eastern belief.
Although many people think of Sheol as basically a realm of 'nothingness' (or perhaps nothing more than metaphorical for non-existence itself), we really just don't have much good direct data to pinpoint what ancient Israelites really thought of it. But I think there's some slight indication that it wasn't quite the realm of 'nothingness' that people have made it out to be. Other ancient Near Eastern afterlife schemes do have some notion of reward and punishment, in various ways.
In any case, whether it was due to Near Eastern influence or Indo-European influence, by the time we get to the 3rd century BCE or so (and probably before this), we do clearly see a more developed idea of underworld realms (again, see the books of Enoch, as mentioned in my previous comment).
Unfortunately I can't say much more on this at the moment (gotta hit the sack) - but you might have more luck over at /r/AcademicBiblical in the meantime.