   "Sarcophagi"             
[28] "Blocks"                  "Marble.type"             "Other.cargo"            
[31] "Hull.remains"            "Shipboard.paraphernalia" "Ship.equipment"         
[34] "Estimated.tonnage"       "Amphora.type"           </code></pre>
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<p>A system of maritime routes is found in variables <code>Place.of.origin</code> and <code>Place.of.destination</code>, which correspond to columns 20 to 21 in <code>sw</code>. This edge list needs some t