Calendar

All correct, including the always-worthwhile correction of "after death." Dionysius, computing Easter tables in Rome, replaced the era of Diocletian ("the persecutor") with years reckoned ab incarnatione Domini; Bede's popularity spread the system; Charlemagne's chancery institutionalised it. Two additions complete the picture:

Dionysius probably got the year wrong – and scholarship says so freely. Matthew's nativity requires Herod the Great (died 4 BCE); Luke's census points at 6 CE; the datable anchor is Luke 3:1's "fifteenth year of Tiberius" (28/29 CE) with Jesus "about thirty." The standard critical estimate therefore puts the birth c. 6–4 BCE – meaning Jesus was born "before Christ" on Dionysius's own numbering. This is in every reference work, and it teaches the method: a sixth-century computist's arithmetic is checked against first-century administrative pegs (Herod's death, Tiberius's accession, Pilate's prefecture 26–36) and found a few years off. The pegs are the evidence; the era is bookkeeping. Nobody dates the existence of anyone by the label on the timeline – a miscalculated era no more unmakes its reference point than Rome's confused ab urbe condita reckonings unmake the city.

The weekday names make the useful control case. Yes: English weekdays enshrine Germanic and Roman gods, just as December 25 was assigned in the fourth century (the Gospels give no birth date, and Christmas's placement near the solstice festivals is conventional church history, not a discovery – the standard scholarly discussions are happy to say "we don't know Jesus's birthday and the date is liturgical"). Cultures wrap their calendars around gods, heroes and rulers indiscriminately: Wednesday no more attests Odin's historicity than AD attests the incarnation – and, symmetrically, no more refutes it. July is named for Julius Caesar and August for Augustus: same mechanism, real men. Calendars record what a culture honoured, not what existed; the existence question is settled by first-century documents, and those have their own pages here – Paul☦, Josephus, Tacitus.