The SBLHS 2 §8.1.2 recommends the use of all caps without periods in abbreviations of chronological eras (see also CMS §9.35):
| AD | anno Domini (in the year of our Lord) |
| AH | anno Hegirae (in the year of [Muhammad’s] Hegira) |
| BC | before Christ |
| BCE | before the Common Era |
| BP | before the present |
| CE | Common Era |
Note that, when spelled out, “Common Era” is capitalized. In this, we follow the CMS §§8.72–73 in capitalizing many traditional, premodern historical and cultural periods:
the Augustan Age
the Bronze Age (Early Bronze Age, Middle Bronze Age, etc.)
the Common Era
the Counter-Reformation
the Enlightenment
the Iron Age (Iron I, Iron II, Iron III)
the Middle Ages (the High Middle Ages, but early Middle Ages, late Middle Ages)
the Renaissance
the Reformation
Note: We capitalize the words early and middle before Bronze Age because the Early Bronze Age and Middle Bronze Age are traditionally defined archaeological periods.
Aside from these traditional periods, we follow the CMS in recommending a caps-down style wherever possible (see CMS §8.71). Thus:
ancient Greece
antiquity
early Christianity
early Judaism
imperial Rome
late antiquity, late antique
the Amoraic period
the Byzantine period
the church age
the classical period
the Gaonic period
the Hellenistic period
the patriarchal period/age
the Persian period
the postapostolic era
the postbiblical era
the postexilic period
the preexilic period
the rabbinic period
the Roman period
the Tannaitic period
In the latter list, Amoraic, Roman, Christianity, Hellenistic, and the like are capitalized because they are the proper names of peoples (see CMS §8.37), cities or countries (see CMS §8.44), religions (see CMS §8.95), or proper adjectives derived from proper nouns (see CMS §5.67).
In SBLHS 2 §4.3.6, gaon and gaonic are lowercased. The term gaon should be lowercased when it is used as a generic term. Like Amoraim and Tannaim, however, the plural form, preferred spelling Geonim, should be capitalized because it is the proper name of an identifiable group (like Pharisees, Sadducees, Zealots, Essenes). The proper adjective derived from Geonim should also be capitalized. We recommend the following spelling and capitalization norms:
gaon (office), but Saadiah Gaon (title used with name)
Geonic
Geonim
SBL Handbook of Style 