Green’s Dictionary of Slang

Ludgate Prison, mainly used for debtors.

1617		J. Taylor ‘Iacke a Lent’ in Works (1869) I 119: Twenty citizens [...] shall take vp their lodgings in Luds vnlucky gate.
1619		J. Taylor ‘A Kicksey Winsey’ in Works (1869) II 38: ’Twas their unhappy fate / The Counters, or King Lud’s unlucky gate.