Upper level
1. top stone
2. canal/water conduit
3. arch
4. platform of separation

Middle level
5. span
6. support
7. ornament
8. projecting blocks supported the scaffolding during construction
9. road

Lower level
10. span
11. pier/breaker of the flow
12. river
 

The canal (2) through which the water flowed with the top stone (1).