Over the weekend, architects and city planners revealed an ambitious proposal for the redevelopment of New Haven’s ninth square. It calls, fittingly, for a sunny, tree-lined, Roman piazza in place of the dark, ill-fated Coliseum — scheduled for demolition later this year — and a host of welcome strategies for attracting and accommodating people in New Haven. All the ingredients of a successful urban renewal program seem to be budgeted in the more than $400 million design, which unlike past efforts, actually seems capable of revitalizing part of this city.

The proposal calls for a 100,000 square foot conference and convention center to bring traffic through New Haven. It makes room for a 300-room hotel where visitors can sleep; 54,000 square feet of retail space where they can shop; and 1,500 new parking spaces split between above- and below-ground lots, where they can park their cars. There will be five new apartment buildings along the piazza’s perimeter — much needed rental housing downtown — and a new Long Wharf Theatre facility on North Frontage Road. And, enticing more young people to the district, Gateway Community College will relocate one of its two campuses to the old Macy’s department store building –a cautionary relic of the ill-fated urban renewal program that saw the construction of the Coliseum in the first place.

When longtime New Haven mayor Richard C. Lee built the Coliseum more than 30 years ago, it was the finishing touch to more than a decade of intense urban planning. Like much of the rest of Lee’s noble but misguided campaign to remake downtown New Haven, the Coliseum was built with soaring optimism and the intention of bringing people and prosperity back to a moribund district. A hop, skip and a very dark leap away from the Green, it stands now more like a mausoleum than a center of city life.

This proposal, prepared by Herbert S. Newman and Partners at the request of Gov. Rowland, realizes Lee’s vision for New Haven in many of the ways Lee’s own plan did not. The real challenge in this case will be if Mayor DeStefano is as successful in securing funding as Lee was. Rowland has withheld the $10 million in state aid necessary for knocking down the Coliseum until he sees plans for what will go in its place. The plans themselves are just what the city needs — and worthy of Rowland’s signature — but the source of the funding to support the construction, set to begin as soon as the Coliseum crumbles, is not so clear.

Money has not been secured for any of the projects, each of which is to be handled separately, and the convention center promises to demand an operating subsidy from the already strapped city budget. The proposal has the right idea, and is worth pursuing, but this city is familiar with ambitious designs that have fallen short of their promises. In the coming months, New Haven will need the right financial planning in addition to the right city plan.