Sentence:  The <WSD>principal</WSD> treasure of ths department, however, is the Stele of Hammurabi (1792—1750 B.C.), king of the first Babylonian kingdom, a basalt cylinder 2.25m/7ft 5in. inscribed with Hammurabi′s laws written in Akkadian in cuneiform script. 
Meaning of the word marked with <WSD> tags:  Primary; most important.