It’s hard to believe that such a small bridge could wreak so much havoc.

But that’s exactly what happened when the two-lane Cook’s Bridge — connecting Central Ave in Needham with Elliot Street in Newton — was determined to be failing and closed this summer.

Commuters who used the bridge to get to and from work knew the July closing would pose a hardship. And fears that the shut-down would hurt businesses on both side of the Charles were well-founded, with some businesses reporting significant shortfalls.

Less expected were the mind-numbing backups — along Needham Street and Highland Avenue, Nonantum and Kendrick streets in the N2 Innovation District and Route 9 — all created by the diverted traffic.

Five months later, Cook’s Bridge has been re-opened, slightly ahead of schedule.

The Chamber, in partnership with Newton, Needham officials and residents, are planning a parade across the bridge to celebrate the reconnecting of the two communities on Saturday, Dec. 17 from 11 a.m. to noon.

The free event will include a marching band, kazoos, refreshments and a visit from Santa Claus.

A three-span stone masonry arch, Cooks Bridge was originally constructed in 1844. In 1897, the bridge was widened by 15 feet on the upstream (southern) side for the Boston & Newton Street Railway. A sidewalk was built on new concrete piers on the downstream side in about 1970. In 1991, the downstream sidewalk was reconstructed and an upstream sidewalk was added.

Somewhere along the way the bridge was listed as a historical structure on state and federal registers.

But in recent years the bridge had started to deteriorate. Fire trucks and other heavy vehicles were banned from using it. Engineers warned that it was only a matter of time before state inspectors would close the bridge to all traffic.

The rehabilitation project, which was funded by the two municipalities, had two overarching goals: reinforce the bridge to last another 75 years and turn it into a pedestrian destination. The repair design used reinforced concrete on top of the original stones, to prevent them from moving but to maintain the historic façade.

While the bridge is now fully open to traffic with one open sidewalk, the second sidewalk and other cosmetic work is set to be completed in the spring.