Valu lui Traian (historical name: Hasancea, Turkish: Hasançay) is a commune in Constanța County, Northern Dobruja, Romania.
The commune was established in 1897, under the name Hasancea. In 1925 it was renamed Valu lui Traian (Trajan's Wall), after the vallum located nearby. In 1967, the village of Valea Seacă (historical name: Omurcea, Turkish: Ömürçay) was merged into Valu lui Traian, now the commune's only village.
The Constanța metropolitan area, is a metropolitan area, established in 2007, that includes the municipality of Constanța, the towns of Năvodari, Ovidiu, Eforie, Murfatlar, Techirghiol and 8 communes: Mihail Kogălniceanu, Cumpăna, Valu lui Traian, Lumina, Tuzla, Agigea, Corbu and Poarta Albă. According to the 2021 census, it has a population of 415,695, in an area consisting of 16% of Constanța County.
As defined by Eurostat, with 420,241 residents (as of 2015), the Constanța functional urban area is the third most populous in Romania.