Why was this made and how was it used?
The seal of the Emperor Henry of Flanders authenticated imperial documents. It was used as we today use a signature on financial and legal documents. However, it is also a visual characterization of the individual it represents. The emperor's religious authority is displayed on the obverse side, where we see Henry as an enthroned figure, and his military expertise is highlighted on the reverse side, where we see him as a warrior on horseback.
Seals have been used for millennia, long before the crusades began. From the ancient world to the crusader period and beyond, seals have been used to authenticate documents, to prove to the recipient and to a wider audience that the attached document is the true and legal word of whoever sent it. Interestingly, a seal actually has no authority by itself -- its authority comes from a society who recognize the validity of seals.
