Schulze| W. "The Byzantine 'Eagle' Countermark - Re-attributed from Egypt to Palestine" in INR volume 4 (2009), p. 113 - 120.
During the turbulent years of the Arab conquest of Syria in the 30s of the seventh century CE, a series of Byzantine countermarks was in use. One of them, the'eagle' countermark, has been attributed for a long time to Egypt and may now be re-attributed to Palestine on the basis of new evidence. This countermark may have been applied on old and worn Byzantine coins in order to revalue them during the siege of Caesarea (637–640 CE).
Available online: https://www.academia.edu/6830710/The_Byzantine_Eagle_Countermark_Re-attributed_from_Egypt_to_Palestine