The 1998 PBS series, From Jesus to Christ: The First Christians continues to impress me, and I'll still point people to the legacy website. Good to keep bookmarked if you study theology, teach in church, or preach.
A particular page called Why Did Christianity Succeed? The Rise of Christianity: A Sociologist Considers History -- excerpted from Rodney Stark's 1996 The Rise of Christianity -- stands out because he questions the wisdom that Christianity became dominant over pagan cultus because of Constantine's establishment. Rather, Christianity seems to have won a popular place that Constantine consolidated. Also, Stark contends it wasn't miracles or martyrs that made people Christians but a kind of administration that people could up hold (he cites the ruinous costs of pagan religious exercises), a leadership that was close to the common people, and the claims that Christianity (and Judaism) made towards conversion rather than mere adherence (itself a product of how deity is understood.)
It don't lift the article up in a "look at those silly Pagans; their religion fell apart" way, but because the same thing could very easily happen to Christianity as we know it in the United States. When the faith takes on a corporate (as in business) gloss, a reputation for high costs and endless fund-raising, and a pandering uncertainty about where it stands, the future doesn't look good.