Its harbour, from which Milesian ships set forth to found over 100 colonies during the seventh and eighth centuries b.c. , is now a frog-filled marsh.
The Milesian ships never created colonies as their mission was to only trade. 
mnli hypothesis: The Milesian ships never created colonies as their mission was to only trade.  premise: Its harbour, from which Milesian ships set forth to found over 100 colonies during the seventh and eighth centuries b.c. , is now a frog-filled marsh.