The orangery originated from the Renaissance gardens of Italy, when glass-making technology enabled sufficient expanses of clear glass to be produced. In the north, the Dutch led the way in developing expanses of window glass in orangeries, though the engravings illustrating Dutch manuals showed solid roofs, whether beamed or vaulted, and in providing stove heat rather than open fires. This soon created a situation where orangeries became symbols of status among the wealthy. The glazed roof, which afforded sunlight to plants that were not dormant, was a development of the early nineteenth century. The orangery at Dyrham Park, Gloucestershire, which had been provided with a slate roof as originally built about 1702, was given a glazed one about a hundred years later, after Humphrey Repton remarked that it was dark; though it was built to shelter oranges, it has always simply been called the "greenhouse" in modern times.

The orangery, however, was not just a greenhouse but a symbol of prestige and wealth and a feature of the garden, in the same way as a summerhouse, folly or "Grecian temple". Owners would conduct their guests there on tours of the garden to admire not only the fruits within but the architecture without. Often the orangery would contain fountains, grottos, and an area in which to entertain in inclement weather.

(source wikipedia)