This is the 946th most frequent German word.
lag
"Lag" is the past tense of "liegen," meaning "lay" or "was situated."
Here, 'lag' is used as the past tense of 'liegen', describing the stationary position of the subject, the book.
Das Buch lag auf dem Tisch.
The book was lying on the table.
In this instance, 'lag' is part of the phrase 'lag an', where 'an' often describes a cause or reason.
Es lag an der fehlerhaften Installation.
It was due to the faulty installation.
Here, 'lag' metaphorically expresses a prevailing state or condition related to the subject, the city.