Chan Chan

Gotta love chaotic covers like this one! From a 6v set these 1968 green stamps feature carved adobe from the expansive ancient city of Chan Chan (c.850-1470).
Thank you Juan!
Thank you Juan! 'Pro-restoration of Chan Chan' issue. This is no./170 of 4000 FDCs.
Thank you Josef! Another numbered fdc #2316. Issued November 11 1987. 
Thank you Guy! #4 shows a similar relief to above stamp.