The tetrarchs (from the Greek words for "Four rules") were the four co-rulers that governed the Roman Empire as long as <a href="//commons.wikimedia.org/wiki/Diocletian" class="mw-redirect" title="Diocletian">Diocletian</a>'s reform lasted. Here they were portraied embracing, in sign of harmony, in a <a href="//commons.wikimedia.org/wiki/Porphyry" class="mw-redirect" title="Porphyry">porphyry</a> sculpture dating from the 4th century, produced in Asia Minor, today on a corner of <a href="//commons.wikimedia.org/wiki/Category:San_Marco_(Venice)" title="Category:San Marco (Venice)">Saint Mark's</a> in <a href="//commons.wikimedia.org/wiki/Venice" class="mw-redirect" title="Venice">Venice</a>, next to the "<a href="//commons.wikimedia.org/wiki/Porta_della_Carta" class="mw-redirect" title="Porta della Carta">Porta della Carta</a>". Picture by <a href="//commons.wikimedia.org/wiki/User:G.dallorto" title="User:G.dallorto">Giovanni Dall'Orto</a>, August 12, 2007.
<a href="//commons.wikimedia.org/wiki/User:G.dallorto" title="User:G.dallorto">G.dallorto</a>
CC BY-SA 2.5 it
<span class="int-own-work" lang="en">Own work</span>