Myth of Hestia
In ancient Greece Hestia was the goddess that protected the houses. Every house had an altar where fire was burning day and night. If the fire was extinguished people believed that great misfortune would come to this house.
Altars with fire burning day and night existed also in the temples. If the fire was extinguished people believed that great misfortune will come to the whole city.
In ancient Greek, all states of the time  had colonies. At that time each town  was considered as a different state. The colonies existed because
a) the population of a certain city grew and therefore more land was needed
b) the ships of the time could not travel in bad weather or for long distance without taking new supplies.
c) Not all areas produce the same products. All goods (food, wine, minerals like gold and silver, handicrafts) were moving from the place of production to the place of consumption by the sea, therefore it was crucial for a town to have a "friendly" port close to the place that the goods were produced or consumed.
For all these reasons colonies were established. The settlers, which where the people that would go to create the new city, were taking with them fire from the temple of the mother city (the city from which they left). When arriving in the place where they were going to establish the colony, the first building they were constructing was the temple in which they placed the fire. This was believed to bring good fortune to the new town and its inhabitants. This also stated the relation between the colony and the mother city.