CHICAGO (CBS) — Uber on Sunday became the largest tenant in the Old Post Office as it officially took over space in the building.

Back in August, the rideshare company signed a 10-year lease for nearly half a million square feet at the Old Chicago Main Post Office, which carries a street address of 433 W. Van Buren St. and straddles the Eisenhower Expressway.

Uber will start construction on its new space in the spring.

This will be its second-largest suite of offices in the U.S. behind its space in San Francisco.

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Other tenants signed to move into the Old Post Office include Walgreens and Ferrara Candy.