Assuming you mean 223 A.D., it is the 3rd century. To figure out what the century is, it is one above what seems logical. For example, the 1900's is the 20th century, and the 200's like in your question is the 3rd century.
The 3rd century.
It is in the 3rd century.
3rd century
265 was in the 3rd century.
The 3rd century AD.
3rd century
The 3rd century.
270ad was the 3rd century.
3rd century.
The 3rd century BC.
It is the 3rd century BC.