bivalate, bivallate

In military architecture, a pair of defensive ditches and earth embankments, usually concentric, that surround a mound or medieval fort.
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The better Irish historical record also makes the connections between kingship and enclosures clear--early Irish law tracts describe some kings' seats to have been univallate, bivallate or trivallate ringforts, and there appears to have been a direct correlation between status and the size of the enclosure (e.