This is a Viking key made of steel. It would have been used with a padlock. The design is originally Roman, and the key was made before the wealth and conquest of the Viking Age.
Brick Stamp representing Emperor Theoderic from the Aurelian Wall, which he did repairs on. Apparently there are numerous types of stamp from his reign. To specify, this is Theoderic the Great (there are atleast 5 Theoderics...) Also, this is broken…