Add BCE temporal tags to all documents; add temporal-dating steering doc

civilizations/sumer.md

@@ -4,32 +4,32 @@
 # Sumer
 
 ## Overview
-Sumer was the earliest known civilization in southern Mesopotamia (modern-day southern Iraq), emerging ~4500 BCE and flourishing during the 3rd millennium BCE. It is credited with foundational innovations including writing (cuneiform), urbanization, and codified law.
+Sumer was the earliest known civilization in southern Mesopotamia (modern-day southern Iraq), emerging ~4500 BCE and flourishing during the 3rd millennium BCE. It is credited with foundational innovations including writing (cuneiform), urbanization, and codified law. @t[~4500 BCE]
 
 ## Key Facts
 - Region: Southern Mesopotamia, between the Tigris and Euphrates rivers
-- Period: ~4500–1900 BCE
+- Period: ~4500–1900 BCE @t[4500 BCE..1900 BCE]
 - Major cities: Ur, Uruk, Eridu, Lagash, Nippur, Kish
 - Language: Sumerian (language isolate)
-- Writing system: Cuneiform, developed ~3400 BCE
+- Writing system: Cuneiform, developed ~3400 BCE @t[~3400 BCE]
 - Government: City-states ruled by *lugal* (kings) and *ensi* (governors)
 
 ## Major Periods
-- Ubaid period (~5500–4000 BCE): Proto-urban settlements
-- Uruk period (~4000–3100 BCE): First true cities, invention of writing
-- Early Dynastic period (~2900–2350 BCE): Competing city-states
-- Third Dynasty of Ur (~2112–2004 BCE): Final Sumerian renaissance under Ur-Nammu
+- Ubaid period (~5500–4000 BCE): Proto-urban settlements @t[5500 BCE..4000 BCE]
+- Uruk period (~4000–3100 BCE): First true cities, invention of writing @t[4000 BCE..3100 BCE]
+- Early Dynastic period (~2900–2350 BCE): Competing city-states @t[2900 BCE..2350 BCE]
+- Third Dynasty of Ur (~2112–2004 BCE): Final Sumerian renaissance under Ur-Nammu @t[2112 BCE..2004 BCE]
 
 ## Achievements
-- Invented cuneiform writing ~3400 BCE [^1]
+- Invented cuneiform writing ~3400 BCE @t[~3400 BCE] [^1]
 - Built ziggurats as temple complexes
 - Developed the sexagesimal (base-60) number system
-- Created the earliest known legal code (Code of Ur-Nammu, ~2100 BCE)
+- Created the earliest known legal code (Code of Ur-Nammu, ~2100 BCE) @t[~2100 BCE]
 - Established irrigation agriculture at scale
 - Produced the *Epic of Gilgamesh*, among the earliest literary works [^2]
 
 ## Decline
-Sumer was absorbed by the Akkadian Empire under Sargon of Akkad ~2334 BCE, briefly revived under the Third Dynasty of Ur, and finally eclipsed by the rise of Babylon ~1900 BCE.
+Sumer was absorbed by the Akkadian Empire under Sargon of Akkad ~2334 BCE, briefly revived under the Third Dynasty of Ur, and finally eclipsed by the rise of Babylon ~1900 BCE. @t[~2334 BCE]
 
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 [^1]: Schmandt-Besserat, D. *Before Writing* (1992)