Groups

Introduction

If you have two tiers of stratigraphic grouping in your organisation or project then ‘Groups’ form a higher level and therefore is a higher order interpretative process above the primary grouping (subgroups). The aim of groups in this case is to further simplify particularly complex (often deeper urban) stratigraphic sequences by grouping subgroups. This assists in the broader interpretation of an area. From the perspective of structuring data, groups serve as useful ‘tags’ or conceptual containers for referring to clusters of related stratigraphic subgroups (and associated contexts) in the synthesis of the site.  If it is done properly, tiered grouping can help assemble your stratigraphy into ‘bite-sized chunks’, which are easier to digest and write about. As such stratigraphic groups (and any subgroups nested within them) can be used to feed into understanding land use across a site (if this is being deployed) aiding in the organisation of the stratigraphic narrative and reporting (often forming subsections of a technical stratigraphic summary and phased stratigraphic discussion). Also, because like subgroups, they respect the stratigraphic sequence they can be used to highlight which features might be compared (or ‘lumped’ together) by specialists in their own analysis. Once grouped the stratigraphic matrix can be reduced down into a group matrix diagram.

Methods

In a two-tiered grouping system where subgroups have been deployed, the subgroups can be associated to form higher order ‘Groups’. In this case, the already subgrouped matrix serves as the central reference point for this process. This matrix should be formulated during post-excavation work by considering the aspects of construction, use, and disuse. In cases where such a matrix has not been previously established, it’s essential to create one before proceeding.

The subgroup matrix should have been devised with reference to three main aspects: the stratigraphic relationship of the archaeology, (where possible) spot dates from dateable finds, and the spatial locations of the archaeology. In terms of stratigraphic relationships and spot dates, the group should also reflect the underlying stratigraphic matrix and be organised in descending order of time, with later features at the top and earlier ones below, and sometimes the decision of ‘what cut what’ made on site might need to be reversed based on dateable material evidence. Spatial locations should be arranged such that proximate features are near each other on the matrix, left or right, according to cardinal points, as far as possible.

When preparing for the grouping, it’s important to anticipate the major land use units on the site, as groups should not be split across separate land uses. One must also ensure that the specialists are happy with the spot-dating at the time of reporting (accepting that future work might change the date range of materials). The process of grouping involves reviewing plans and the subgroup matrix and commencing to group together features of a common type and date into numbered groups, taking care not to conflict with land use issues. For instance, pits on one side of a trackway should be grouped separately from those on the other if a functional distinction can be made between two open areas. Similarly, walls of the same date should be grouped separately based on their ultimate land use, (e.g. if they are part of different buildings, or part of a later building modification/phase).

The use of provisional phase plans can be beneficial at this stage, allowing the drawing of conjectural extensions of ditches and buildings, which can present possibilities for what is happening in some of the ‘negative’ spaces on the site. For example, potential routeways or boundaries may suggest themselves as linear negative spaces, while gaps or pockets of ‘negative’ space may hint at possible building plots or areas that were disused due to factors like water-logging or because they overlay an old cemetery.

Once groups are defined and circled or coded on the subgroup matrix or plan (depending on the verticality/horizontality of the stratigraphic sequence) it should be allocated a number in line with the recording protocol for the project and subgroups can be annotated with the relevant group number. Group descriptions should also be added at this stage, and a date-phased group matrix should then be drawn. When group numbers have been allocated for an area a group list should be compiled for reference, which includes the group number, a detailed description and the phase allocation; this list should be appended to your stratigraphic and group narrative.

The group stage is a good time to eliminate all remaining null contexts, such as voided contexts, modern intrusions, repeated contexts, natural deposits, and any others that will not fit into the eventual land use entities.

The groups thus created are essentially the elements that, either individually or in combination, will constitute the land use entities. While simpler sites may bypass the group stage and place groups of subgroups directly into land use entities, it is generally beneficial to complete the group and group matrix stage, especially for complex sites, as it encourages structured thinking. For sites with several areas or any complexity, drawing up a new and date-phased group matrix can be a very helpful tool for the next stage, which is the land use.

Open and Closed Groups

Open and closed stratigraphic groupings is a concept that can play a crucial role in projects where areas of an archaeological site are consistently revisited over time, such as in long-term research projects. This consistent revisiting can span multiple seasons or even years, allowing the stratigraphic records to be refined and reinterpreted as more information is unearthed and understood.

In such scenarios, open stratigraphic groups are sometimes utilised. This approach allows for a more dynamic and evolving interpretation of the site’s stratigraphy. The groups remain ‘open’ to accommodate new findings or reinterpretations over time, thereby facilitating a more fluid understanding of the site’s historical context as the excavation progresses.

Whilst phasing may (and probably will) change subject to further work, stratigraphic groups are supposed to represent a stable tool for stratigraphic and other specialist analysis. To this end it is also important that it is noted when a group is closed. Unlike Phases, groups can often be ‘signed off’ as complete if a large enough area is excavated, although this obviously cannot happen if any of the features within a group extend beyond any limits of excavation. A group is considered closed when all of the possible stratigraphic contexts tied to that group have been excavated and fully recorded. If there is anything left to do in the field for any of these contexts then the group must be left open (the most obvious example being when features extend under the limit of excavation).

However, it’s important to note that the notion of open and closed groupings is not commonly encountered in commercial archaeological contexts. This is typically due to the project-based and time-bound nature of commercial archaeology where areas of the site are not consistently revisited in the same manner as in academic research projects. Instead, in commercial contexts,whilst grouping may remain open to editing at any stage in the stratigraphic analysis prior to publication and archiving, each excavation usually results in a unique, standalone set of records that are interpreted and ultimately grouped without the presumption of revisiting the same area for further work.

What makes a Group (in a two-tiered stratigraphic grouping system)

The definition and interpretation of these groups would often depend on the specific characteristics and context of the archaeological site under investigation. It may also be influenced by organisational and project based vocabularies and protocols. However, following are examples of common entities which might form discrete (second tier) stratigraphic groups, which might be formed by grouping relevant archaeological subgroups,broad examples might include:

1. Domestic Structures Group: This group could be formed by subgroups representing different rooms within a house or different components of a single room (e.g., hearth, floor, wall).
2. Cemetery Group: This group might be composed of subgroups representing individual graves or burial clusters within a cemetery.
3. Fortification Group: This group might include subgroups representing different components of a defensive structure, such as a wall, a gate, or a tower
4. Ceremonial Structures Group: This group could include subgroups representing different parts of a temple, shrine, or other religious or ceremonial structures.
5. Agricultural Activities Group: This group might be formed by subgroups representing evidence of farming activities such as fields, irrigation systems, or crop storage structures.
6. Industrial Activities Group: This group would comprise subgroups representing different components of an industrial site, such as a pottery kiln, a metalworking shop, or a mill.
7. Road and Pathways Group: This group could include subgroups representing different parts of a transportation network, such as roads, bridges, or paths.
8. Waterfront Structures Group: This group could be formed by subgroups representing various features of a waterfront, such as docks, warehouses, or shipyards.
9. Destruction Horizon Group: This group might include subgroups representing widespread destruction debris that will typically seal several earlier groups.
10. Open Space Group: This group could be formed by subgroups representing unoccupied or less structured areas within a settlement, such as courtyards, middens or activity areas. 

Assigning subgroups to groups

If subgroups have been deployed then at some point they will need to be assigned to a higher level ‘Group’. Following is a workflow summary on how to assign subgroups to second-tier stratigraphic groups:

1. Follow the Stratigraphic Sequence: Start at the bottom of the sequence, following the longest strand on the stratigraphic diagram, and then integrate the shorter, ‘floating’ strands before they are sealed.
2. Group Related Subgroups: Place closely related subgroups, such as those representing the construction and use of one building, into one stratigraphic group. Do not include contemporary open areas in the same group, to maintain separate records of different types of land use.
3. Numbering Groups: Establishing a clear numbering system for your stratigraphic groups is crucial, starting from the base of the sequence and progressing upward. This method reflects the proposed chronological order and can vary based on project or organisational protocols.
4. Create a Group Matrix (Sequence Diagram): At this stage, your group matrix should take shape from your existing matrix, which is either your stratigraphic matrix or your subgroup matrix (if you created subgroups). This will provide a clear overview of the stratigraphic sequence and the connections between different archaeological elements.
5. Link Groups to Land Use Synthesis and Diagrams: At this point, consider how the groups can be linked to broader understandings of land use. Develop land use synthesis diagrams that incorporate these stratigraphic groups to visually represent patterns of land use over time.
6. Illustrate Groups: As a final step, produce visual representations or illustrations of these groups (these could be plans or sections). These visual aids will help to communicate the spatial relationships, sequences, and overall narrative of the site.

Some further points to note:

• Dealing with structural alterations through time: If alterations have occurred over a considerable timespan, they form part of different stratigraphic groups, even if they relate to the same structure.
• Handling ‘floating’ subgroups: Compare stratigraphically floating subgroups with events on the longest strand of subgroups. Determine where they could fit in as a group based on their description, surface height, and interpretation. If no clear association can be made, it may be necessary to assign these floating subgroups to a separate group of their own, before the long strand of subgroups is sealed.
• Considering cut features and sealing horizons: Ensure that if a subgroup contains cut features, these features remain visible at the surface of a group. The sealing horizon should be part of the following group and reflect a different kind of land use, to clearly display structural and occupational patterns and assign features a lifespan.
• Handling large-scale debris and demolition: If there is widespread destruction debris that seals several earlier groups, this can form a separate group as part of a destruction horizon. However, if the debris is small and localised, it could be part of the previous group.
• Grouping across discrete trenches or areas: The extent to which grouping should be confined within one trench or extend across multiple trenches, needs to be considered and may relate to factors such as project’s duration, team size, or excavation scale. Notably, in the case of the latter, grouping may well extend across separate strands of matrix.
• Remaining fluid and open to changes: Keep the grouping process as fluid as possible to allow for future phases of post-excavation where finds, samples, and dendrochronology dates may be combined. Avoid ‘locking’ features together in groups that may be difficult to reanalyse later.