Floral tributes have been placed in memory of men and women who were accused of being witches.
Colchester Castle played host to witchcraft trials between 1560 and 1680, and suspected witches were held there awaiting their fate.
Kathleen Savage, of Colchester Pagan Network, said an appeal was made at the group's annual East Anglian Conference for people to honour the suspected witches.
She said: "People are apologising at the moment to the families of slaves and to Holocaust victims, and we thought these people deserved a memorial too.
"They were often dragged from their beds in the middle of the night to be brought to the castle for their trial.
"We suggested the idea at the conference on Saturday and when I went past the castle yesterday, I was amazed to see people had actually put flowers outside - they had even put labels on for specific people. I was overwhelmed by the response."
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