Green’s Dictionary of Slang

1. the vagina; thus fig. the state of chastity or honour.

c.1566		Harman Caveat for Common Cursetours in Viles & Furnivall (1907) 72: And when he had untrussed himself and put down, he began to assault the unsatiable fort.
1600		T. Heywood Edward IV (1874) I 84: I yeelded vp the fort, Wherein lay all the riches of my joy; But yet, sweete Shore, before I yeelded it, I did indure the longst and greatest siege That euer batterd on poor chastity.
1605		Chapman All Fooles I i: I can come To lay no batt’ry to the fort I seek. All passages to it so strongly kept By strait guard of her father.
1615		R. Brathwait Strappado 165: Come then my lad of mettall make resort, Vnto the throne of loue thy Betties fort. There plant thy Cannon siedge her round about. Be sure (my Boy) she cannot long hold out. Erect thy standard, let her tender brest, Be thy pauillion.
1629		J. Shirley Grateful Servant III iv: How many forts they have beleaguered, how many they have taken by battery, how many by composition, and how many by stratagem.
c.1650		‘The Ladies’ Fort Besieged’ in Wardroper (1969) 83: Assault her but often, you’ll carry the fort.
a.1660		song in Wardroper (1969) 70: He talked so wity and wooed so pretty / None could deny, / But needs must yield the fort up, / Gude faith, and so did I!
1661		‘Peter Aretine’ Strange Newes 3: Wandring-W—. I spread my shrouds, unveil my Cabinet [...] and open the pure Linen Curtains that hang before my chief Fortress.
1673		Holborn Drollery 59: This did encourage Venus Slave To enter the Enchanted Cave; But being enter’d at the Gates, His warlike Courage soon Abates: But had he known the manner how To Storm a Fort as he should do, No doubt he’d Storm’d it in his Shirt.
1688		C. Sackville ‘Faithful Catalogue’ in Lord Poems on Affairs of State (1968) IV 209: [She] will tumble down, At first assault surrenders up the town; But no kind conqueror has yet thought fit To make it his belov’d imperial seat; That batter’d fort, which they with ease deceive, Pillag’d and sack’d, to the next foe they leave.
1690		‘Teague’ Teagueland Jests II 160: He stormed the Fort and took it [...] he boldly entred [sic] again, and took Possession.
1709		N. Ward Compleat and Humorous Account of Remarkable Clubs (1756) 291: Or that your Want of Courage spoils her Sport, / And makes your fearful to attack the Fort.
1719		in D’Urfey Pills to Purge Melancholy VI 276: There’s ne’er a lass in aw Scotland ... That has her Fort so bravely Mann’d.
1723		C. Walker Authentick Memoirs of Sally Salisbury 35: He is too enterprizing a Warrior that way, and happening not long since to Storm a Rotten Fort.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1896		Farmer Vocabula Amatoria (1966) 56: Casemate, f. The female pudendum; ‘the fort’.

2. the anus [? self-censorship / mis-reading].

1886

Western Times 28 May 2/4: Fort — the fundament.