diff --git a/Gemfile b/Gemfile
index 740bd8bf834c1945c1d58ca048135e2bc2730353..331eaae4dfb01621676f7f7dbc209ce6dea5e76e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -56,11 +56,6 @@ gem 'sass'
 # needs special branch for rails 4.2
 gem 'prototype-rails', github: 'rails/prototype-rails', branch: '4.2'
 
-# legacy helper for form_remote_for and link_to_remote
-# there's only a 0.0.0 version out there it seems
-gem 'prototype_legacy_helper', '0.0.0',
-    github: 'rails/prototype_legacy_helper'
-
 # Full text search for the database
 gem 'thinking-sphinx', '~> 3.4.2'
 
diff --git a/Gemfile.lock b/Gemfile.lock
index bbce8ec60487c6f9aa10f74438f2e8aab14b3084..fadfb0c9e308017a832f2c21f2bb9f3fc125c421 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,12 +6,6 @@ GIT
     prototype-rails (4.0.0)
       rails (~> 4.0)
 
-GIT
-  remote: https://github.com/rails/prototype_legacy_helper.git
-  revision: a2cd95c3e3c1a4f7a9566efdab5ce59c886cb05f
-  specs:
-    prototype_legacy_helper (0.0.0)
-
 PATH
   remote: vendor/gems/riseuplabs-greencloth-0.1
   specs:
@@ -278,7 +272,6 @@ DEPENDENCIES
   phantomjs-binaries (~> 2.1.1)
   poltergeist (~> 1.5)
   prototype-rails!
-  prototype_legacy_helper (= 0.0.0)!
   rails (~> 4.2.10)
   rails-html-sanitizer (~> 1.0.4)
   rake (~> 10.0)
diff --git a/app/controllers/wiki/diffs_controller.rb b/app/controllers/wiki/diffs_controller.rb
deleted file mode 100644
index 4267c1e4c58614001cfcd0b51ce966d220d7e08b..0000000000000000000000000000000000000000
--- a/app/controllers/wiki/diffs_controller.rb
+++ /dev/null
@@ -1,43 +0,0 @@
-class Wiki::DiffsController < Wiki::BaseController
-  guard show: :may_show_wiki_diff?
-
-  helper 'wikis/versions'
-  javascript :wiki
-
-  def show
-    if @old
-      @diff = Crabgrass::Wiki::HTMLDiff.diff(@old.body_html, @new.body_html)
-    else
-      render template: '/wikis/versions/show'
-    end
-  end
-
-  protected
-
-  # making sure the version is available for the permission
-  def fetch_wiki
-    super
-    if params[:page]
-      fetch_versions_with_page
-    else
-      fetch_versions_without_page
-    end
-  rescue Wiki::VersionNotFoundError => err
-    error err
-    redirect_to wiki_versions_path(@wiki)
-  end
-
-  def fetch_versions_without_page
-    old_id, new_id = params[:id].split('-')
-    @old = @wiki.find_version(old_id) unless old_id.blank?
-    @version = @new = @wiki.find_version(new_id)
-    params[:page] = @wiki.page_for_version(@new)
-    @versions = @wiki.versions.most_recent.paginate(pagination_params)
-  end
-
-  def fetch_versions_with_page
-    @versions = @wiki.versions.most_recent.paginate(pagination_params)
-    @version = @new = @versions[0]
-    @old = @versions[1]
-  end
-end
diff --git a/app/helpers/wikis/diffs_helper.rb b/app/helpers/wikis/diffs_helper.rb
deleted file mode 100644
index cb68f619ed5ece7e78051124c7b2ea469b88927b..0000000000000000000000000000000000000000
--- a/app/helpers/wikis/diffs_helper.rb
+++ /dev/null
@@ -1,48 +0,0 @@
-module Wikis::DiffsHelper
-  # not sure this is what we want.
-  # it's currently required by the Wiki::DiffsControllerTest
-  # but we might have remove diffs from the UI for now.
-  def back_to_wiki_link
-    wiki_path(@wiki)
-  end
-
-  # some translations still have the %{user} and %{when} key.
-  # TODO clean them up and remove params here.
-  def comparing_changes_header
-    :comparing_changes_header.t(old_version: old_version_tag,
-                                new_version: new_version_tag,
-                                user: content_tag(:b, link_to_user(@new.user)),
-                                when: content_tag(:i, full_time(@new.updated_at))).html_safe
-  end
-
-  def old_version_tag
-    content_tag :del, short_description(@old, true),
-                class: 'diffmod', style: 'padding: 1px 4px;'
-  end
-
-  def new_version_tag
-    content_tag :ins, short_description(@new, true),
-                class: 'diffins', style: 'padding: 1px 4px;'
-  end
-
-  def diff_previous_link
-    if previous = @old.previous
-      link_to_remote (LARROW + :prev_change.t).html_safe,
-                     url: wiki_diff_path(@wiki, @old.diff_id),
-                     method: :get
-    else
-      content_tag :span, (LARROW + :prev_change.t).html_safe, class: 'disabled'
-    end
-  end
-
-  def diff_next_link
-    if next_version = @new.next
-      link_to_remote (:next_change.t + RARROW).html_safe,
-                     url: wiki_diff_path(@wiki, next_version.diff_id),
-                     method: :get
-    else
-      content_tag :span, (:next_change.t + RARROW).html_safe, class: 'disabled'
-    end
-  end
-
-end
diff --git a/app/views/wiki/diffs/_show.html.haml b/app/views/wiki/diffs/_show.html.haml
deleted file mode 100644
index 7994bc31126a5ae2054491702eec6a7f21599f96..0000000000000000000000000000000000000000
--- a/app/views/wiki/diffs/_show.html.haml
+++ /dev/null
@@ -1,11 +0,0 @@
-.info
-  = comparing_changes_header
-  %br/
-  %i= :changes_made.t when: full_time(@new.updated_at)
-
-.pagination
-  = diff_previous_link
-  = diff_next_link
-
-.diff.wiki
-  =@diff
diff --git a/config/locales/en/wiki.yml b/config/locales/en/wiki.yml
index bc1d17c5c91ceb37d2799d41aea1583f61c88b15..bb9dfbc20ebe35e5423687bc7641d3f31c5009f2 100644
--- a/config/locales/en/wiki.yml
+++ b/config/locales/en/wiki.yml
@@ -6,7 +6,6 @@ en:
   cant_find_wiki_section: "Can't find wiki section %{section}"
   changes_made: "Changes made %{when}."
   changes_might_be_overwritten: "Your changes might be overwritten."
-  comparing_changes_header: "Comparing changes between %{old_version} and %{new_version}."
   diff_link: "view changes"
   edit_wiki: "Edit Wiki"
   force_save_button: "Break Lock and Save"
diff --git a/config/routes.rb b/config/routes.rb
index 1bf31c06c85cafe5faf7c0dd9e9bd8170fe6b400..f988d2d8a1cb287601b56d7dcd268b3fed8e3281 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -219,7 +219,6 @@ Crabgrass::Application.routes.draw do
         post 'revert'
       end
     end
-    resources :diffs, only: [:show]
   end
 
   ##
diff --git a/extensions/pages/wiki_page/test/functional/wiki/diffs_controller_test.rb b/extensions/pages/wiki_page/test/functional/wiki/diffs_controller_test.rb
deleted file mode 100644
index c94bf15502df1c3135784e8dd64959f9113f6767..0000000000000000000000000000000000000000
--- a/extensions/pages/wiki_page/test/functional/wiki/diffs_controller_test.rb
+++ /dev/null
@@ -1,20 +0,0 @@
-require 'test_helper'
-
-class Wiki::DiffsControllerTest < ActionController::TestCase
-  fixtures :pages, :users, 'user/participations', :wikis, :groups
-
-  def test_diff
-    login_as :orange
-
-    (1..5).zip(%i[orange yellow blue red purple]).each do |i, user|
-      pages(:wiki).data.update_section!(:document, users(user), i, format('text %d for the wiki', i))
-    end
-
-    get :show, wiki_id: pages(:wiki).data_id, id: '4-5'
-    assert_response :success
-
-    assert_equal assigns(:wiki).versions.reload.find_by_version(4).body_html, assigns(:old).body_html
-    assert_equal assigns(:wiki).versions.reload.find_by_version(5).body_html, assigns(:new).body_html
-    assert assigns(:diff).length > 10, 'difftext should contain something substantial'
-  end
-end