The author is Tim Whitmarsh and the subtitle is Augustus, Empire and the Making of Christianity.  This is the most important book on the history of Christianity I have read in a long time, and it is also an important work in Roman history.  Yet also fun and extremely readable.  Excerpt:

The story I have told so far has emphasised the fit between Christianity and the Greek world of the early Roman Empire; I have given relatively little space to conflict.  That has been quite deliberate.  One of the commonest misconceptions about the early Roman Empire is that it was a time of ceaseless and inevitable suppression of virtuous Christians by a brutal governmental machine.  This is a myth that has roots in antiquity itself, and has been pumped systematically into western popular culture since the nineteenth centuury.  It is a remarkably durable myth, because it is both emotionally seductive and ideologically powerful.  The idea that virtuous Christians were engaged in endless conflict with the Roman state makes for great narrative.  But the reality is more banal: most Christians were fully integrated into Roman society, and no more or less harassed than anyone else…

My argument has been, rather, that Christianity could not have come into being in anything like the form we know it without the revolutionary impact of Augustus’ political reforms.  It was this seismic change that fundamentally transformed Mediterranean thought…The most dramatic effect of the Augustan swirl was Christianity itself: a breakaway Judaean sect led by brilliant entrepreneurs who understood the opportunities offered by the new political dispensation, and rapidly reshaped their ideas to suit new audiences.

Definitely recommended, and not only to Christians and Romans.