Coffins have been a part of burial rituals since the beginning of human civilization, and their cultural significance is profound. Today, they can even be used as a source of decorating on holidays like Halloween. Their purpose is vitally important, both as a means of interring the dead and as a cultural expression of how we acknowledge and revere those who came before us. As a symbol of death, they can often invoke morbid or ghoulish feelings, but they also act as a measure of comfort: conveying us and those we love between this life and whatever comes afterward.
Coffins have been discovered dating back to the very earliest civilizations. The ancient Egyptians used sarcophagi to inter their pharaohs, while the Greeks would often bury their dead in clay urns. Stone coffins appeared in Europe during the rise of Christianity, gradually giving way to wooden and metal coffins commonly used today. Japan used round barrel-shaped coffins during the same period, often made of wood as well. In 19th century America, many coffins were mass produced, and thus often adopted a rectangular shape rather than the "wide at the shoulders, narrow at the feet" design of earlier cultures. Funeral directors at the time also began referring to coffins as "caskets," as a way of reducing the negative connotations associated with them. The sealed coffin attained perfection in the early 1940s, allowing the body within to remain free from decay for decades or longer.
A coffin's original significance was likely a practical one: by holding a corpse within sealed walls, it could help prevent the spread of decay and disease. In some cultures, it could also hold gifts and belongings, which the occupant could use in whatever afterlife his society believed in. The position of the corpse in a coffin may give clues to the culture's feelings about death: the "eternal slumber" notion adopted by modern Western cultures is contrasted by cultures where the body is placed in a sitting or fetal position. The surface of the coffin could be decorated with hieroglyphics or religious symbols, signifying either the culture's particular beliefs, or some aspect of life which was important to the occupant. Because ancient coffins could help preserve their contents, they are an invaluable archaeological tool in deducing how a given culture lived and what many of their spiritual practices entailed.
Modern coffins are often made of steel, though coffins made of polished wood are common as well. The primary selling point of steel is preservation, keeping the corpse free not only from decay, but from carrion vermin as well. They can be mass produced on assembly lines, very similar to the way cars are produced. The engineering is such that the seal between top and bottom is airtight: capable of being opened for display at funerals and then shut up tight once the body is interred. The outside can be painted to suit the buyer's tastes, and coffin makers have noted that popular casket colors seem to roughly parallel those of current automobiles.
Wooden coffins are not always as durable as metal coffins, but they can be more useful in other situations. Most notably, they work well when the occupant wishes to be cremated. (Sometimes cheaper materials such as cardboard or pressboard are used to cremate a body, with a more elaborate facade used at the funeral.) Wooden coffins are also perceived as more ecologically friendly, especially those made of bamboo or similar lightweight materials. They can be rendered airtight the way steel coffins can, though rarely as completely. Indeed, in some cases, they allow for cleaner decomposition, since bacteria can pass through wood more easily and thus remove noxious decompositional discharge more readily.
Along with headstones, coffins have now been ingrained in popular culture as symbols of death and decay. The iconic figure of Count Dracula is forever associated with rising out of his coffin, while the Goth subculture has embraced it as a key part of its visual iconography. Coffin nails are said to have supernatural powers in some religions, and suburbanites decorate their lawns or homes with replicas on Halloween. The image serves to remind us of our own mortality, and thus to celebrate life as a precious and finite thing.