Final answer:
The name of Spain's longest river is the Tagus River. It flows across central Spain and Portugal with a length of approximately 1,007 kilometers.
Step-by-step explanation:
The name of Spain's longest river is the Tagus River (also known as the Tajo River). It flows across central Spain and Portugal, and has a total length of approximately 1,007 kilometers (626 miles). The Tagus River is an important water resource for both countries and has influenced the development of cities and agriculture along its course.
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