This study investigated the plant species composition growing on a two thousand year old Roman wall in the village of Silchester, Hampshire, UK. The factors controlling differences in species composition were investigated. The wall, which is 1.5 miles in perimeter, was systematically sampled using quadrats inside, outside and on top of the wall itself. The data was statistically analysed using the Shannon Index of Diversity to determine the diversity of various sections of the wall. The results indicated that the main controlling factors governing the differences in the species diversity and composition on the wall were aspect, the type of restoration material and also the time since restoration, concurring with the literature researched . The analysis indicated that the sections of the wall facing in a north-east direction had the highest species diversity. These sections were also restored using lime mortar, a soft, porous bonding material. The sections of the wall facing in an eastward direction had the lowest species diversity. These sections have been left unrestored in recent times (i.e. during the last two centuries). However, the effects of aspect, restoration material and time could not be differentiated from each other because management of the wall and therefore the materials used in its restoration, were directly related to aspect. It was concluded that lime mortar is preferable for management as it lacks harmful effects on the wall construction, and also on the plants themselves.
