Pleiades Data Structure

Pleiades content is organized into three types of "information resource": places, locations, and names.


In Pleiades, places are conceptual entities. They are objects of thought, speech, or writing, not tangible, mappable points on the earth’s surface. Even though they are usually tied closely to some aspect or feature of the physical world — a sea, a bay, a river, a mountain range, a pass, a road, a settlement, or an ethnic region — They have no spatial or temporal attributes of their own. Their primary quality is that, in the words of Yi-fu Tuan [1], they are "constructed by human experience."

A place can be known only through a name mentioned an ancient source, without any surviving material correlate; conversely, an archaeological site can be understood as a place even if we do not know what it was called in antiquity. Even a modern city known or presumed to be located atop an ancient settlement is a place for Pleiades purposes. Places may be no larger than a family dwelling or as big as an empire, be temporally enduring or fleeting. They may expand, contract and evolve over time. A place may be unnamed, unlocated, falsely attested or even mythical.

Locations and Names

The spatial aspects of Pleiades places (i.e., latitude and longitude coordinates), as well as their ancient and modern names, are addressed through two other conceptual entities: locations and names.

Locations connect places to coordinates in space. A location identifies a specific area of interest on the earth's surface that is associated with a place during a particular date range. A place can contain multiple locations. Depending on the state of the evidence, the association between location and place may vary in certainty; some places, attested by name in ancient sources, may have no associated location at all because modern scholarship cannot pinpoint reliably the ancient site or area in question.

Names are also connected with places. A name reflects the identity of a place in human language, not its physical location in the landscape. Names have no spatial coordinates, but they are always annotated with the time period(s) of the textual source(s) in which they are attested. As with locations, a single place can have multiple names, but an individual name can be associated with one and only one place (even if the same sequence of characters is attested as a name for another place as well).

Database Structure

The Pleiades system documents and describes each of these three conceptual entities using a corresponding "information resource". Information resources are bundles of structured data that are similar in function to records in a database or index cards in a card file. Each place resource contains the name and location resources with which it is associated. This encapsulation is expressed in the layout of information on the Pleiades website, and in the hierarchical structure of the Uniform Resource Identifiers (URIs: web addresses) Pleiades assigns to each resource. Each place resource has a corresponding web page in Pleiades, and each of these place pages links to individual pages for all the name and location resources that have been associated with it.

The structure and implementation of the Pleiades database are described in more detail in the Pleiades Data Model document.

Example: Condercum

Consider the Roman fort of Condercum (at modern Benwell, near Hadrian's Wall in the United Kingdom). Pleiades has assigned the permanent identifying number 89150 to this conceptual place. Entering the Pleiades URI in a browser yields the corresponding place page. Links to individual pages for the associated locations ("Centerpoint of the ancient site", "Boundary of fort walls") and names ("Benwell", "Condercum") are listed under the appropriate headings. The map on the place page is derived from the contained location resources.