Cistercian numerals (See https://en.wikipedia.org/wiki/The_Ciphers_of_the_Monks)

cistercian.rb

# frozen_string_literal: true

module Cistercian
  LINE = %w[■ ■ ■].freeze
  CENTER_DOT = '   ■   '
  GLYPHS = [
    ['   ',
     '   ',
     '   '],
    ['■■■',
     '   ',
     '   '],
    ['   ',
     '   ',
     '■■■'],
    ['■  ',
     ' ■ ',
     '  ■'],
    ['  ■',
     ' ■ ',
     '■  '],
    ['■■■',
     ' ■ ',
     '■  '],
    ['  ■',
     '  ■',
     '  ■'],
    ['■■■',
     '  ■',
     '  ■'],
    ['  ■',
     '  ■',
     '■■■'],
    ['■■■',
     '  ■',
     '■■■']
  ].each(&:freeze).freeze

  module_function

  def cistercian(number)
    raise ArgumentError, 'Impossibly low' if number.negative?
    raise ArgumentError, 'Impossibly high' if number > 9999

    ones, tens, hundreds, thousands = number.digits

    lines = [
      *upper_glyphs(ones: ones, tens: tens),
      CENTER_DOT,
      *lower_glyphs(hundreds: hundreds, thousands: thousands)
    ]

    lines.join "\n"
  end

  def print_cistercian(number)
    puts cistercian(number)
  end

  private_class_method def upper_glyphs(ones:, tens:)
    GLYPHS.fetch(tens.to_i)
          .map(&:reverse)
          .zip(LINE, GLYPHS.fetch(ones.to_i))
          .map(&:join)
  end

  private_class_method def lower_glyphs(hundreds:, thousands:)
    GLYPHS.fetch(thousands.to_i)
          .map(&:reverse)
          .reverse
          .zip(LINE, GLYPHS.fetch(hundreds.to_i).reverse)
          .map(&:join)
  end
end

example.rb

require_relative 'cistercian'

include Cistercian

print_cistercian 5042
■  ■
 ■ ■
  ■■■■■
   ■
  ■■
 ■ ■
■■■■


print_cistercian 9999
■■■■■■■
■  ■  ■
■■■■■■■
   ■
■■■■■■■
■  ■  ■
■■■■■■■