As a follow-up to this week's blog post, How to handle Serial Sites, I'd like to do a deep dive into two aspects to see whether it is worth labelling the serial sites with a "type' (as Digits suggested in the blog post comments).

The two questions I'd like to have answered (for myself at least) are:
1. How do the UNESCO World Heritage guidelines and ICOMOS/IUCN look at serial nominations - are there "rules" that may not be broken, and is there some kind of categorization by type?
2. Will the list of 7 "types" that I listed in the blog post hold up when challenged by more examples?

Operational Guidelines of the World Heritage Convention
This is what they specify regarding serial nominations:

Definition and Rationale (Paragraph 137)
A serial property consists of two or more distinct, geographically separated component parts that collectively demonstrate Outstanding Universal Value (OUV).
To be considered a valid serial nomination, the component parts must share clearly defined links, which typically fall into one of three visual or thematic frameworks:
1. Cultural / Historical: Components belong to the same socio-cultural group, historical period, architectural style, or artistic movement (e.g., The Architectural Work of Le Corbusier).
2. Geographical / Ecological: Components belong to the same biogeographical province, morpho-climatic region, or continuous eco-system (e.g., Ancient and Primeval Beech Forests of the Carpathians and Other Regions of Europe).
3. Thematic / Functional: Components share a distinct functional relationship or single integrated concept (e.g., Routes of Santiago de Compostela, Prehistoric Pile Dwellings around the Alps).

Core Justification & Integrity Requirements (Paragraph 138)
The guidelines set strict conditions to prevent bloated or arbitrary serial nominations:
- Collective OUV: The property as a whole—not the individual components on their own—must possess Outstanding Universal Value.
- Necessary Components: Each included component must contribute directly to the overall OUV in a substantial, demonstrable way.
- Cohesion & Proportionality: The overall series must be logical, cohesive, and manageable. Unnecessary components that do not add distinct value to the OUV should be excluded.
- Avoidance of Over-representation: A serial nomination should not simply be a collection of similar sites without a unifying narrative or justification.

3. Management and Protection (Paragraph 139 & Paragraph 114)
Managing a multi-site property—especially across administrative or national borders—presents unique logistical challenges. The guidelines mandate:
Overall Management Framework: In addition to site-specific management plans for individual components, a serial property must have an overarching joint management system or framework.
Coordination Mechanisms: Clear communication channels, shared monitoring standards, and coordinated administrative bodies must be established among all responsible authorities.
Protection: Each individual component part must be adequately protected under national, regional, or local legislation and feature an effective buffer zone where applicable.

Checklist used by ICOMOS and IUCN in evaluating serial sites
When evaluating a serial nomination, technical desk reviewers and field mission experts from ICOMOS and IUCN are asked to answer the following key questions:

1. Is a Serial Approach Justified? Is the whole greater than the sum of its parts? Does combining these components express an Outstanding Universal Value (OUV) that no single site could convey on its own? Is there a clear, demonstrable link? Are the components connected by a well-defined thematic, cultural, functional, evolutionary, or ecological framework? Could the site be nominated as a single continuous site instead? If the components are contiguous or close enough to be drawn inside a single boundary, a serial nomination is deemed unjustified.

2. Are All Component Parts Necessary? Does every component contribute to the OUV? Experts review the component list line-by-line. If a specific component part does not explicitly add unique attributes to the overall narrative, ICOMOS/IUCN will recommend its removal. Is the selection representative and well-rationed? Does the nomination include the best or most significant examples of the phenomenon, rather than an arbitrary or opportunistic gathering of sites?

3. Is the Series Cohesive and Complete? Are there major gaps in the series? (e.g., If a serial nomination claims to represent a specific historical trade route, architectural movement, or migratory flyway, are critical sites missing from the selection?)Does it avoid over-representation? Does the series suffer from redundant components that merely repeat what other parts already express without adding value?

4. Can the Serial Property Be Effectively Managed? Is there an Overarching Management Framework? Beyond individual local management plans, is there a functional joint management committee or coordinating body linking all parts together? Are monitoring and protection standardized? Do all components—regardless of differing local or international jurisdictions—enforce compatible legal protection and conservation standards?

As far as I can see, this is the only reference to the composition of serial nominations.

And nothing is said about the hierarchy among components, as long as they all contribute to the OUV and are "necessary" (explicitly add unique attributes to the overall narrative). They expect "the best or most significant examples of the phenomenon, rather than an arbitrary or opportunistic gathering of sites"

Tomorrow, I will have a closer look at the 10 sites with the highest number of components, and whether they can be assigned to one of the seven "types":
Rock Art of the Mediterranean Basin 715
Frontiers of the Roman Empire 442
Dacian Limes 277
Funerary and memory sites of the First World War 139
Qhapaq Ñan 137
St. Petersburg 112
Prehistoric Pile Dwellings 111
Nord-Pas de Calais Mining Basin 109
Lower German Limes 102
Primeval Beech Forests 93

St. Petersburg really stands out here. Where other major cities were inscribed as a whole, they opted for a serial approach with 112 sites (ICOMOS notes 136?). It seems to me that here we have the issue that they inscribed a huge urban center where there were multiple components who could have been their own WHS. They could have done one for the downtown core, one for the palaces located far from the urban core, and one for the fortresses (at least those are the three themes that I see). I don't know if they have or will ever do that again. There's no central theme to these diseparate pieces as far as I can tell. I feel like ICOMOS was so eager to recommend this WHS that they didn't really really question why it was being nominated in that way. Their own 1990 advisory document even starts with "The inclusion of Leningrad on the World Heritage List is so obvious that any detailed justification seems superfluous."

Note that WHC decision 34COM 7B.95 did recommend that it be recognized as a single site.