- Purpose-built structure, other than a bollard, to prevent vehicle or pedestrian access to a road or site, for example concrete blocks to obstruct vehicles accessing beaches on the north-east coast for illegal sea-coaling.
- English Heritage
- http://creativecommons.org/licenses/by/3.0 (FISH Thesaurus of Monument Types)
- http://www.english-heritage.org.uk (FISH Thesaurus of Monument Types)
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