"Did they like to make things as hard as possible for themselves?" asked
Gerda with interest.

"Not so much as they liked to make it as hard as possible for their
enemies," said Herr Ekman. "Centuries ago, hunters and fishermen built
their rude huts on the wooded islands at the outlet of Mälar Lake. They
often found it convenient to slip away from their pursuers among these
islands; but they were not always successful, for their settlements on
the site of the present city were repeatedly destroyed by hostile
tribes."

"Why didn't they build fortifications on the islands and hold the enemy
at bay?" questioned Birger.

"They were too busy sailing off to foreign lands," answered his father.
"Fleet after fleet of Viking ships sailed out of the bays of Sweden,
manned by the bravest sailors the world has ever known; and they swooped
down upon the tribes of Europe, fighting and conquering them with the
strength of giants and the glee of children."

"It was Birger Jarl who built the first walls and towers to protect the
city," spoke Gerda. "I remember learning it in my history lesson."

"Yes," her father replied; "good old Earl Birger, who ruled the Swedes in
the thirteenth century, saw how important such fortifications would be,
and so he locked up the Mälar Lake from hostile fleets by building walls
and towers around one of the islands and making it his capital."

"There is an old folk-song in one of my books which always reminds me of