What does"At le Grau du Rai"mean in this indention below? le grau du rai and Aigues Mortes are the cities in France.why "at" & why not "in"?

THEY WERE LIVING at Ie Grau du Rai then and the hotel was on, a canal that ran from the walled city of Aigues Mortes straight down to the sea. They could see the towers of Aigues Mortes across the low plain of the Cam argue and they rode there on, their bicycles at some time of nearly every day along the white road... show more THEY WERE LIVING at Ie Grau du Rai then and the hotel was on,
a canal that ran from the walled city of Aigues Mortes straight
down to the sea. They could see the towers of Aigues Mortes
across the low plain of the Cam argue and they rode there on,
their bicycles at some time of nearly every day along the white
road that bordered the canal. In the evenings and the mornings
when there was a rising tide sea bass would come into it and
they would see the mullet jumping wildly to escape from the
bass and, watch the sweJling bulge of the water as the bass attacked.
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