The city of Venice originated as a collection of lagoon communities banded together for mutual defence from the Lombards, Huns and other invading peoples as the power of the Western Roman Empire dwindled in northern Italy. These lagoon communities formed the republic in 697 AD and elected their first Doge. The first Doges all attempted to create a dynastic succession but all ultimately failed. However Venice enjoyed a long period of peace throughout this time and slowly built a complex system of canals, bridges, bulwarks, fortifications, and stone buildings. Thus Venice began to rely on the sea for defense and offence and slowly began to extend its force south into the Adriatic. With the crusades Venice found new trading opportunities in the Levant. This prosperity brought envy and the Byz