Paper flames were taped to the exterior of buildings throughout Portland’s Old Port on Wednesday to commemorate the 150th anniversary of a fire that destroyed a third of the city’s commercial district.

The Great Fire of 1866 was ignited July 4th by a child’s firecracker on Portland’s waterfront. Stoked by a strong southwest wind and aided by drought conditions, the fire quickly spread across a mile-long swath of the peninsula, devouring more than 1,500 buildings and 58 city streets and scorching 200 acres. Four people died and more than 10,000 people were rendered homeless.

At the time, it was the most destructive fire in U.S. history.

To mark the fire’s anniversary, Greater Portland Landmarks placed about 500 color photocopies of flames to mark the fire’s border and several areas within the Old Port that were destroyed. The group of 22 board members, docents and volunteers also marked about a dozen buildings that survived the blaze, said Advocacy Director Julie Larry. “We wanted to bring attention to the extensive area of the downtown that was impacted by the fire in a more hands-on way than just looking at a map,” Larry said. She said the Time and Temperature Building on Congress Street will also be flashing the message “Fire 1866” to bring attention to the catastrophe, which continues to shape Portland today.

As a result of the fire, uniform standards for fire insurance were developed and Portland finally moved forward with a project to connect Portland to Sebago Lake some 17 miles away for a steady water supply, rather than relying on wells, cisterns and reservoirs. Many of the buildings standing in the Old Port today were built in the months after the fire, in many cases using the same bricks salvaged from the buildings damaged and destroyed by the fire. After the fire, the residential neighborhoods on the East End and West End began to take shape and Lincoln Park was created as a fire break.

The flames were inspired by the familiar red hearts that have been posted all around Portland each Valentine’s Day for the past several decades by an anonymous person or group known only as the Valentine’s Day Bandit.

The paper flames are just one of the ways that historians are marking the fire anniversary:

 On Wednesday, the Maine Historical Society opened an exhibit featuring poignant imagery of the fire’s destruction to show how it dramatically affected the development of the city. The exhibit, “Images of Destruction: Remembering the Great Portland Fire of 1866,” is curated by Maine State Historian Earle G. Shettleworth Jr. Historical society members and children age 5 and under can see the exhibit at 489 Congress St. for free. Admission is $8 for adults; $7 for seniors, AAA members and students; and $2 for children between the ages of 6 and 17.

• On Monday, July 4th, local historian Herb Adams will emcee an event beginning at 4:15 p.m. in Monument Square. It will include the ringing of bells at 4:41 p.m. by the nearby First Parish Church, which survived the fire, and a reading of 1866-era letters about the fire. The Portland Fire Department’s Michael Daicy, who co-authored “Portland’s Greatest Conflagration: The 1866 Fire Disaster,” and Bob Greene, a descendant of William Wilberforce Ruby, who reported the blaze, will also be on hand.

• Also Monday, the Portland Symphony Orchestra will explore the theme of fire during its performance of the “Stars and Stripes Spectacular” on the Eastern Promenade.

• On July 6, Shettleworth will give an hour-long lecture on “The Great Fire of 1866” at the Maine Historical Society starting at 6 p.m. Shettleworth will examine the cause of the fire and why it was so destructive, as well as its impact on residents and how the city recovered. Admission is $5 for members and $10 for nonmembers. For more information, call 774-1822.