brick, which absorb and retain solar heat and then slowly release it, raising the temperature against the wall, allowing peaches, nectarines, and grapes to be grown as espaliers against south-facing walls as far north as southeast Great Britain and southern Ireland. The ability of a well-designed walled garden to create widely varying stable environments is illustrated by this description of the rock garden in the Jardin des Plantes in Paris’ 5ème arrondissement, where over 2,000 species from a variety of climate zones ranging from mountainous to Mediterranean are grown within a few acres: Heated walls A number of walled gardens in Britain have a hot wall or fruit wall, a hollow wall with a central cavity, or openings in the wall on the side facing towards the garden, so that fires could be lit inside the wall to provide additional heat to protect the fruit growing against the wall. Heat would escape into the garden through these openings, and the smoke from the fires would be directed upwards through chimneys or flues. This kind of hollow wall is found at Croxteth Hall in Liverpool (England), and Eglinton Country Park and Dunmore House, both in Scotland. At Croome Court an 18th-century cavity wall had a number of small furnaces to supply gentle heat (see below). In the 1800s, such walls were lined with pipes and connected to a boiler, as at Bank Hall in Bretherton. Design The traditional design of a walled garden, split into four quarters separated by paths, and a wellhead or pool at the centre, dates back to the very earliest gardens of Persia. The hortus conclusus or "enclosed garden" of High Medieval Europe was more typically enclosed by hedges or fencing, or the arcades of a cloister; though some protection from weather and effective protection from straying animals was afforded, these were not specifically walled gardens. Kitchen gardens In the United Kingdom, many country houses had walled kitchen gardens which were distinct from decorative gardens. One acre of a kitchen garden was expected to provide enough produce to feed twelve people, and these gardens ranged in size from one acre up to twenty or thirty acres depending on the size of the household. The largest gardens served extremely large households, for example, the royal kitchen garden at Windsor was built for Queen Victoria in 1844 and initially occupied twenty two acres, but was enlarged to thirty one