Revetment, Pisa

Pisa revetments were basically composed of a compressed mixture of moistened vegetable and inert soils. Soil containing a high proportion of organic matter was mixed with clay, a little cut straw thrown in to keep the revetment from cracking as it dried, and just enough water added to make the mixture bond into a solid mass when compressed. The pisa mass was to be formed along the foot of the interior crest in layers two feet wide (front to rear) and one foot high; the initial layer served as an anchoring foundation and was formed in a trench excavated on the parapet side of the foot of the interior slope. Formation of a well bonded pisa wall required the use of formwork (a movable wooden frame) otherwise an attempt to compress it would tend to cause the pisa to spread out, get mix with the soil of the parapet, and become quite useless for the purpose of forming a mass with load bearing capability. An uncompressed revetment could be built up and shaped using a common shovel. As more layers were added the pisa would not need to be dry, rather, a certain degree of moisture was required in preceding layers for sufficient bonding with the next layer to take place. But the whole mass would need to be dry and solid before soil of the body of the parapet could be packed against it. In general a Pisa revetment would be given a shape that did not differ from most masonry revetments; exposed side angled to follow the slope of the interior slope and the side abutting the body of the parapet either on a vertical line or slightly tapered toward the top.

As might be imagined, constructing a pisa revetment was a rather slow and tedious process compared to other types of revetments. Descriptions of this type of revetment do not suggest that it was any better than a sod revetment; certainly its construction was more difficult and time consuming. This type of material was also used to construct houses in dry climates (it was considered a form of masonry), so there would be little concern for its ability to resist the pressure of the parapet and withstand most weather conditions, if well covered by a layer of grass. However effective and durable Pisa revetments might have been, the lack of evidence for its use in any well described fortifications suggests that it was not considered an important option when choosing a revetment.

[This page originally appeared as a Detailed Notes Page on the old Civil War Field Fortifications Website.]

January, 2004