The chapter house was the second most important building in the monastery range after the church. It was here that the monks met every day to discuss abbey business and to listen to a chapter from the Rule of St Benedict. The monks sat on stone benches around the walls as shown in the first picture showing the ruins of the chapter house at Rievaulx. It was here also that punishments were metered out to erring monks, important visitors greeted and Visitations conducted. It was here also that the abbots and monks of monasteries across the land surrendered their properties into the hands of Cromwell’s agents.
Burton and Kerr (page 80) emphasise how unusual the chapter house is at Rievaulx. Instead of being rectangular it has an apse (semi-circular end). It was also large enough to accommodate the lay brothers as well as the choir monks. The chapter house was built during the time of Abbot Aelred (abbot -1147-1167) but the shrine to Sir William of Rievaulx who was Aelred’s predecessor can still be seen behind a window of the chapter house.
Indeed in the earlier chapter houses it is perfectly normal to find the tombs of abbots as well as pavements bearing reference to patrons, even tombs of patrons in some cases. On a more prosaic level in Cistercian chapter houses libraries in the form of book cupboards built into the walls can also be found.
As with much else about monasteries the chapter house changed according to the period in which it was built. Early chapter houses are rectangular ground floor affairs beneath the dormitory but they became increasingly ornate as the medieval period advanced. The chapter house became a separate vaulted building, some with apses and others, which took on a polygon shape- sometimes the original rectangular chapter house became an outer room leading to the chapter house which projected out of the east range. Many chapter houses are separate from the church, with a slype or alleyway between the church and the chapter house but in other places, such as Chester the chapter house adjoins the church. Some chapter houses such as the ones at Southwell are heavily decorated. In Southwell it’s possible to spend hours in the chapter house looking for green men. Foliate heads of all sizes peer at you from the masonry where as at Wells, as the two photographs in this paragraph show, the vaulted ceiling and lantern of glasswork will have you craning your neck. 
Burton, Janet and Kerr, Julie (2011) The Cistercians in the Middle Ages (Monastic Orders). Woodbridge: Boydell and Brewer,
Green men, sometimes known as Jack-in-the-Green, are strange leafy faces. Sometimes the face depicted is very clearly human sprouting leaves, often oak, from their mouths. Other green men are more foliage than person or can be seen wearing leafy masks that cover most of their features. If not oak leaves then the foliage often looks like hawthorn. Sometimes the leaves are realistic and on other occasions they are much more stylized. In some carvings the green man is alone, in others his foliage has attracted the attention of birds and strange beasts. Sometimes, like the capital from York Minster shown at the start of this blog, the green man is triple-faced. There’s a similar, though less friendly looking, tri-faced green man on a misericord in Cartmel Abbey the image at the end). It’s not just men either, beasts including cats sprout leaves from their stone perches in churches and cathedrals across the country.