diff --git a/Gemfile b/Gemfile
index 78d01cbd..a4e9cc70 100644
--- a/Gemfile
+++ b/Gemfile
@@ -32,7 +32,6 @@ gem 'slim', '~> 4'
 gem 'rdoc'
 gem 'kramdown'
 gem 'markaby'
-gem 'radius'
 gem 'asciidoctor'
 gem 'liquid'
 gem 'rabl'
diff --git a/Rakefile b/Rakefile
index f48ae4b3..3fb9707f 100644
--- a/Rakefile
+++ b/Rakefile
@@ -31,7 +31,7 @@ end
 
 Rake::TestTask.new(:"test:core") do |t|
   core_tests = %w[base delegator encoding extensions filter
-     helpers mapped_error middleware radius rdoc
+     helpers mapped_error middleware rdoc
      readme request response result route_added_hook
      routing server settings sinatra static templates]
   t.test_files = core_tests.map {|n| "test/#{n}_test.rb"}
diff --git a/lib/sinatra/base.rb b/lib/sinatra/base.rb
index 727ea68f..90b1075c 100644
--- a/lib/sinatra/base.rb
+++ b/lib/sinatra/base.rb
@@ -733,10 +733,6 @@ module Sinatra
       render :asciidoc, template, options, locals
     end
 
-    def radius(template, options = {}, locals = {})
-      render :radius, template, options, locals
-    end
-
     def markaby(template = nil, options = {}, locals = {}, &block)
       render_ruby(:mab, template, options, locals, &block)
     end
diff --git a/sinatra-contrib/lib/sinatra/engine_tracking.rb b/sinatra-contrib/lib/sinatra/engine_tracking.rb
index c1432239..6709d880 100644
--- a/sinatra-contrib/lib/sinatra/engine_tracking.rb
+++ b/sinatra-contrib/lib/sinatra/engine_tracking.rb
@@ -45,11 +45,6 @@ module Sinatra
       @current_engine == :rdoc
     end
 
-    # @return [Boolean] Returns true if current engine is `:radius.
-    def radius?
-      @current_engine == :radius
-    end
-
     # @return [Boolean] Returns true if current engine is `:markaby`.
     def markaby?
       @current_engine == :markaby
diff --git a/sinatra-contrib/lib/sinatra/namespace.rb b/sinatra-contrib/lib/sinatra/namespace.rb
index 5ff90b9e..157a965b 100644
--- a/sinatra-contrib/lib/sinatra/namespace.rb
+++ b/sinatra-contrib/lib/sinatra/namespace.rb
@@ -226,7 +226,7 @@ module Sinatra
 
       ALLOWED_ENGINES = [
         :erb, :erubi, :haml, :hamlit, :builder, :nokogiri,
-        :liquid, :markdown, :rdoc, :asciidoc, :radius, :markaby,
+        :liquid, :markdown, :rdoc, :asciidoc, :markaby,
         :rabl, :slim, :yajl
       ]
 
diff --git a/sinatra-contrib/lib/sinatra/respond_with.rb b/sinatra-contrib/lib/sinatra/respond_with.rb
index 77e136e9..91c3391c 100644
--- a/sinatra-contrib/lib/sinatra/respond_with.rb
+++ b/sinatra-contrib/lib/sinatra/respond_with.rb
@@ -238,7 +238,7 @@ module Sinatra
     def self.engines
       engines = {
         :xml  => [:builder, :nokogiri],
-        :html => [:erb, :erubi, :haml, :hamlit, :slim, :liquid, :radius,
+        :html => [:erb, :erubi, :haml, :hamlit, :slim, :liquid,
           :mab, :markdown, :rdoc],
         :all =>  (Sinatra::Templates.instance_methods.map(&:to_sym) +
           [:mab] - [:find_template, :markaby]),
diff --git a/sinatra-contrib/sinatra-contrib.gemspec b/sinatra-contrib/sinatra-contrib.gemspec
index b3854f80..858b6ff7 100644
--- a/sinatra-contrib/sinatra-contrib.gemspec
+++ b/sinatra-contrib/sinatra-contrib.gemspec
@@ -50,7 +50,6 @@ EOF
   s.add_development_dependency "liquid"
   s.add_development_dependency "redcarpet"
   s.add_development_dependency "asciidoctor"
-  s.add_development_dependency "radius"
   s.add_development_dependency "nokogiri"
   s.add_development_dependency "markaby"
   s.add_development_dependency "rake", "< 11"
diff --git a/sinatra-contrib/spec/content_for_spec.rb b/sinatra-contrib/spec/content_for_spec.rb
index 56ca8d6d..1ba5485d 100644
--- a/sinatra-contrib/spec/content_for_spec.rb
+++ b/sinatra-contrib/spec/content_for_spec.rb
@@ -90,7 +90,7 @@ RSpec.describe Sinatra::ContentFor do
     end
   end
 
-  # TODO: liquid radius markaby builder nokogiri
+  # TODO: liquid markaby builder nokogiri
   engines = %w[erb erubi haml hamlit slim]
 
   engines.each do |inner|
diff --git a/test/radius_test.rb b/test/radius_test.rb
deleted file mode 100644
index 8c20608c..00000000
--- a/test/radius_test.rb
+++ /dev/null
@@ -1,59 +0,0 @@
-require File.expand_path('helper', __dir__)
-
-begin
-require 'radius'
-
-class RadiusTest < Minitest::Test
-  def radius_app(&block)
-    mock_app do
-      set :views, __dir__ + '/views'
-      get('/', &block)
-    end
-    get '/'
-  end
-
-  it 'renders inline radius strings' do
-    radius_app { radius '<h1>Hiya</h1>' }
-    assert ok?
-    assert_equal "<h1>Hiya</h1>", body
-  end
-
-  it 'renders .radius files in views path' do
-    radius_app { radius :hello }
-    assert ok?
-    assert_equal "<h1>Hello From Radius</h1>\n", body
-  end
-
-  it "renders with inline layouts" do
-    mock_app do
-      layout { "<h1>THIS. IS. <r:yield /></h1>" }
-      get('/') { radius '<EM>SPARTA</EM>' }
-    end
-    get '/'
-    assert ok?
-    assert_equal "<h1>THIS. IS. <EM>SPARTA</EM></h1>", body
-  end
-
-  it "renders with file layouts" do
-    radius_app { radius 'Hello World', :layout => :layout2 }
-    assert ok?
-    assert_equal "<h1>Radius Layout!</h1>\n<p>Hello World</p>\n", body
-  end
-
-  it "raises error if template not found" do
-    mock_app { get('/') { radius :no_such_template } }
-    assert_raises(Errno::ENOENT) { get('/') }
-  end
-
-  it "allows passing locals" do
-    radius_app {
-      radius '<r:value />', :locals => { :value => 'foo' }
-    }
-    assert ok?
-    assert_equal 'foo', body
-  end
-end
-
-rescue LoadError
-  warn "#{$!}: skipping radius tests"
-end
diff --git a/test/views/hello.radius b/test/views/hello.radius
deleted file mode 100644
index 98e35f37..00000000
--- a/test/views/hello.radius
+++ /dev/null
@@ -1 +0,0 @@
-<h1>Hello From Radius</h1>
diff --git a/test/views/layout2.radius b/test/views/layout2.radius
deleted file mode 100644
index 57a06c04..00000000
--- a/test/views/layout2.radius
+++ /dev/null
@@ -1,2 +0,0 @@
-<h1>Radius Layout!</h1>
-<p><r:yield /></p>