Last year, Portland's William Kaven Architecture and Kaven + Co. grabbed headlines when it unveiled its proposal for redevelopment of the United States Post Office site in the Pearl District. The firm pitched a pair of massive towers with a connecting skybridge that would be the tallest buildings in the Pacific Northwest.

This week, the firm moved forward with its plans for the towers by submitting a formal proposal to Prosper Portland, the city's development commission.

According to the plan, the two buildings would be linked by "a glass-enclosed botanical bridge spanning 236 feet across the North Park Blocks some 680 feet in the air, providing dramatic aerial views of the entire city."

The buildings would take the place of the soon-to-be-demolished main post office, which occupies some of the most-prized real estate in Northwest Portland. The site is at the west end of the Broadway Bridge, directly across Northwest Broadway from Union Station.

The location makes it ideal for a transportation hub, potentially high-speed rail or future public transportation innovations.

The development, which is being called the "Broadway Corridor," would feature a combination of residential, office and retail space spread over approximately 5 million square feet.

According to a press release, the development would also include an indoor market facing the North Park Blocks, a museum, a reflecting pool, and a glass-covered park that could be enjoyed year-round, regardless of the weather.

While the proposal is compelling, it's anything but a sure thing. Prosper Portland won't unveil its shortlist of proposals for the post office site until later this spring. William Kaven would need to get approval from the city to build the skyscrapers, since current height restrictions for the area cap buildings at 400 feet.

The developers can expect opposition from Pearl District residents, who complained after the initial plans went public last fall that the skyscrapers would be out of proportion with the rest of the neighborhood.

Construction at the site is scheduled to begin in 2019.

-- Grant Butler

503-221-8566; @grantbutler