Pope Francis on Monday hit out at "offensive words" spoken against the Amazon's indigenous people, noting that a feather headdress is no more ridiculous than hats worn at the Vatican.
"I was pained to hear, right here, a sarcastic comment about a pious man with feathers on his head who brought an offering," the pope said at the opening of a synod focused on the Amazon's poverty-stricken and isolated indigenous communities.
"Tell me what's the difference between having feathers on your head and the three-peaked hat worn by certain officials in our dicasters (Vatican ministries)?" the pope said to loud applause.
The three-week synod, or assembly, unites 184 bishops, including 113 from the nine countries of the pan-Amazon region, including Brazil.
Representatives of indigenous peoples, some with their heads adorned with coloured feathers, are attending the synod, with many gathering in Saint Peter's Square on Monday.
Before an audience of around 250 people, the Argentine pontiff decried "offensive words" used about indigenous peoples, and rejected reductive or destructive "ideological colonisations".
The working document for the synod, known as the "instrumentum laboris", denounces in scathing terms social injustices and crimes, including murders, and suggests a Church action plan.
The document has been criticised by ultra-conservative Roman Catholics, but the pope called Monday on the gathered bishops to feel free to draw up their own final document.
He called the document "a martyr text destined for destruction", prompting laughter from the audience, before the synod got down to work.