Final answer:
The Sumerian city-states were actively engaged in long-distance trade, which is exemplified by the use of lapis lazuli from the Indus valley in their artwork such as the Standard of Ur.
Step-by-step explanation:
Trade in Ancient Sumer
The mention of lapis lazuli being used on the Standard of Ur and originating from beyond the Zagros Mountains indicates that the Sumerian city-states engaged in extensive trade. This is corroborated by historical findings that Sumerian merchants established trade with the Indus valley, exchanging goods such as agricultural products for precious stones like lapis lazuli and carnelian. Evidence suggests that this trade was part of a more significant network that stretched across the Middle East and into India.
The complexity of managing these trade networks required a strong administrative class and contributed to a period of artistic flourishing and the creation of luxurious items, like the mosaic inlays on the Standard of Ur. Thus, the presence of lapis lazuli in Sumerian art is a testament to the long-distance trade networks and the economic prowess of these early city-states.