Brewer's: Black Maria
The black van which conveys prisoners from the police courts to jail. The French call a mud-barge a “Marie-salope.” The tradition is that the van referred to was so called from Maria Lee, a negress, who kept a sailors' boarding house in Boston. She was a woman of such great size and strength that the unruly stood in dread of her, and when constables required help, it was a common thing to send for Black Maria, who soon collared the refractory and led them to the lock-up. So a prison-van was called a “Black Maria.”
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