BARCELONA—Catalan independence activists want to revitalize their movement with a more eye-catching protest than a mass street rally staged a year ago: a 400-kilometer (249-mile) human chain traversing Catalonia from the Pyrenees Mountains to the Mediterranean Sea.

Secessionists in Spain's richest region are counting on the Sept. 11 spectacle, dubbed the Catalan Way Toward Independence, to help them recapture lost political momentum ahead of what could be a decisive year for their cause.

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