Victorian London - Districts - Adelphi Arches 

    The dead body of a female having one morning been discovered, it was currently reported that the assassin was in concealment in the "dark arches;" the police - from information received - were convinced of it, and the authorities, having a mind to probe the mystery, organised search parties, which scattered amongst the labyrinths, and eventually emerged no nearer an elucidation than before.
    Passages, it was asserted, led to various exits on the river bank, and extended in an easterly direction to Whitefriars, all of which in later years have been gradually filled up till now nothing more pernicious than a peaceful beer-store a few yard from the entrance and an occasional board-man who ought to be traversing the street, give signs of vitality to what was once a sink of iniquity. 
    It is refreshing after this weird retrospect to turn to the modern Adelphi Terrace, where years ago I participated in many enjoyable reunions. Here each Sunday night such lively company as the late Kate Vaughan and her husband, Freddy Wellesley, Billy Hill, Marius, Florence St. John, Sweet Nell Hazel, and other vestals congregated; whilst the "Savages" have made it their headquarters, and can lean over the balcony without risking typhoid, and eventually cross the Strand at no greater risk than an invitation to air their French.

'One of the Old Brigade' (Donald Shaw), London in the Sixties, 1908

ADELPHI (THE) (Map 7.) - Comprises three or four street on the south side of the Strand and the handsome Adelphi-ter facing the river, and was built about the middle of the last century by four brothers of the name of Adam, whose names were given to the streets, such as Adam-st, Robert-st, etc. The Adelphi-ter is a desirable place of residence to those who occupation, professional, literary or journalistic, necessitates their living in town. At his house in Adelphi-ter David Garrick died in 1779. The Savage Club, literary, social and musical, is at No. 6. In John-st, Adelphi, is the house of the Society of Arts, which will be found described under its proper heading. The greater part of the Adelphi is built upon arches, which at one time were the chosen resort of thieves and bad characters of every kind. The alterations which were made when the Adelphi arches were put into repair finally closed this modern Alsatia.

Charles Dickens Jr. et al, Dickens Dictionary of London, c.1908 edition 
(no date; based on internal evidence)