Skjaldbreiður, meaning the broad shield in Icelandic, is an Icelandic lava shield formed in one huge and protracted eruption roughly 9,000 years ago. The extensive lava fields which were produced by this eruption, flowed southwards, and formed the basin of Þingvallavatn, Iceland's largest lake, and Þingvellir, the Parliament Plains where the Icelandic national assembly, the Alþing was founded in 930.