This feature has been labeled as deprecated
. The recommended replacement is: archaeological_site=fortification
The reason is documented in Deprecated features
. You are still free to continue to use or interpret this tag as you see fit since OpenStreetMap does not have “banned features”.
Under no circumstances should you (semi-)automatically change “deprecated” tags to something else in the database on a large scale without conforming to the automated edits code of conduct
. Any such change will be reverted.