Horse rings, small brass rings for harnessing horses, were embedded into the curbs of Portland in the days before horse buggies were replaced by cars. Today nobody ties horses to them... unless they're tiny plastic horses.
As historical features, the City of Portland requires construction workers to reinstall the rings when they have to be removed for curb maintenance.
The Horse Project
In Fall 2005, Portland-based artist Scott Wayne Indiana noticed the horse rings serving no practical purpose. So, to reconnect residents with their original use, he began tethering small toy horses to the rings. After a few months, he started a website  and asked for people to help. Since then, many other people, usually anonymously, have taken up the efforts and have adopted their own rings.
- NW Flanders Street and NW 9th Avenue
- SE Cesar E Chavez Boulevard (formerly SE 39th) and SE Taylor
- NW 23rd Avenue and Glisan
- SE 36th Ave and SE Hawthorne Boulevard
- in front of the Delta Cafe on SE Woodstock Boulevard
- NW Hoyt Street and 23rd Avenue.
- Flickr pic:
- Stiefvater, Erick, Where the Sidewalk Ends: Curb Curiosities. OregonLive.com. 2008-04-28.
- Standard Construction Specifications, City of Portland, November 2007. "Salvage any metal horse rings encountered during curb removal. Reinstall horse ring assembly back at the same project stationing or as close as practical. If no new curb is constructed, deliver horse ring assemblies to the City's Maintenance Bureau at Stanton Yard located at 2835 N Kerby Ave."