Doors date back from the ancient Egyptian era. There are paintings which serve as historical records of door architecture. The climate in Egypt was hot and dry enough, that there wasn't any fear of warping. The wood used for doors were just that, slabs of wood on hinges. In most places, due to change of temperature and humidity, doors usually have to be framed.

Other historical records of doors include King Solomon's temple doors. These were made of Olive wood, as were many doors of the past. In India, there were ancient stone doors found. These had pivots on each end, which then fit into sockets. These doors swung open and shut, similar to saloon doors of the old west, but not as quickly.

The Greeks and Romans used many styles of doors; single, double, sliding, or folding. These doors, as well as many others found throughout Europe's past, were made of bronze. This seemed to be the going material for doors, according to historical records.

Doors of today can be made of just about any material found on Earth; wood, metal, plastic, glass, paper, and even fabric. They usually serve the purpose of keeping something in or out. There are interior and exterior doors; animal and people doors, automatic and manual doors, plus real and false doors.

Interior and Exterior -Household doors are usually divided up into interior and exterior groups. An interior door is one found on the inside of a house, while an exterior is exposed to the outer elements on at least one side. Interior doors are found in the bathroom, bedroom, basement (as long as it isn't an outside entrance), and closet. Exterior doors are generally the front and back doors, there might be a door for entering the garage from the outside as well.

Animals and People -People and animals both use doors, but animal doors are usually much simpler than the ones for people. Doors for people have, most of the time, handles or knobs to open them with. Animal doors generally are in the form of a flap, such as in a dog or cat door. These are cut into a larger people door, or sometimes, the wall of a house or building.

Automatic and Manual -There are usually manual doors found in houses. These are the ones that need to have a lever lifted or knob turned, then pulled or pushed by hand in order to open. Automatic doors are a feature that has only been around since 1954, but wasn't first installed until 1960. These were doors for buildings and a mat on the ground which activated the opening. Today, most automatic doors have sensors which trigger the opening. Electric garage door openers were first sold in the year of 1926, today, these also have sensors. Some revolving doors of today are even automatic, instead of the traditional manual style.

Real and False -For the most part, doors are able to be seen, yet sometimes there are doors that lead to nowhere, they don't even open. These are known as 'false' doors. The Egyptians were big on putting these in tombs, in order for the family to have a place to lay offerings. There are even doors made to not look like doors. These are real, but are called 'secret' or 'hidden' doors. Secret doorways can look like a book case in the wall, or a part of the wall itself.

Whether it's a pet door, hidden door, or revolving door, these portals will always be a necessity. Unless humans decide to start leaving gaping holes in their homes, doors aren't something that will likely disappear with the changing times.