Definition of sit down in US English:

sit down

phrasal verb

archaic
  • Encamp outside a city in order to besiege it.

    ‘with a large force he sat down before Ravenna’
    • ‘William drew from his encampment at Cahirconlish, and, confident, of an easy victory, sat down before Limerick.’
    • ‘The Russian army, provided with a full park of artillery for the siege, sat down before it in the middle of May.’