Post hole

In archaeology a posthole or post-hole is a cut feature used to hold a surface timber or stone. They are usually much deeper than they are wide although truncation may not make this apparent. Although the remains of the timber may survive most postholes are mainly recognisable as circular patches of darker earth when viewed in plan. Archaeologists can use their presence to plot the layout of former structures as the holes may define its corners and sides. Construction using postholes is known as earthfast or post in ground construction.

Although a very common structure, and one of the most basic found in archaeology, correct interpretation relies on being able to tell the often subtle differences that distinguish the parts of the posthole. The components of an archaeological posthole are listed in order of creation and, in ideal circumstances, the reverse order of their excavation.

Posthole cut The cut that formed the hole. It is cut from the ground surface level at time of construction. The sides of the hole may be distorted by later pressure on the post (as in the left hand example of the image), or later disturbance. Only careful excavation will be able to distinguish between the original cut profile and any later distortion.

The cut needs to be distinguished from the fill in any detailed stratigraphic analysis, in the same way that any pit fill has to post-date the cutting of the pit, even if by minutes.

Dug up soil Soil excavated from the hole, usually sitting in a pile next to the hole ready for backfilling. Ideal sequence will be that the dug up soil will have material dug through first at the bottom of the pile, with material from deeper down on top of the pile. In optimal situations, the location of dug up soil can be detected adjacent to filled postholes, especially where subsoil differs markedly from the surface material.

Post Normally a round or squared timber placed in the hole. Sometimes a stone may be set in the hole below the post to prevent the post sinking in soft ground or sticks and stones to keep the post properly aligned until it is filled. Many cultures charred their posts to slow down rate of decay in situ. This is sometimes mistaken for burning in situ. Posts may, in modern times, be soaked in creosote or other decay inhibitors or termite preventatives.

The post may survive as an element or have decayed [a postpipe], or been removed. Even if decayed there should be a dark organic stain that matches the original dimensions and extent of the post.

...
Wikipedia