By the 1230s Latins and Greeks were riot short of issues for debate or polemic, but the topic of purgatory did have a novel feel about it. The doctrine seems to emerge on the common agenda fairly suddenly, finding no place, for example, in the wide-ranging list of 104 points of divergence drawn up by the Byzantine prelate, Constantine Stilbès, in the wake of the cruel sack of Constantinople by the Latins in 1204. The subject did, however, establish itself as a hardy perennial, and it is proposed to trace its main ramifications up to the death of Emperor Michael viii in 1282, and then to concentrate on the Council of Ferrara–Florence (1438–9). Without a doubt the debates and the constant attempts at reunion were not conducted in isolation from wider cultural, political and military considerations, the kind of considerations that in 1400 would lead the Byzantine emperor to journey as far as England. But here the emphasis will fall on the theological aspects. Moreover, there were also in play forces of inertia, ignorance and mutual incomprehension difficult to assess rationally. The thirteenth-century friar, Humbert of Romans O.P., in discussing what would make for reunion with the Greeks noted how a schism might be continued simply because it had existed for a long time, just like the feud between Guelf and Ghibelline.