Conversation so far:
Where did Camille Saint-Saëns begin his early career?
On leaving the Conservatoire in 1853, Camille Saint-Saëns accepted the post of organist at the ancient Parisian church of Saint-Merri near the Hôtel de Ville.

Question: How long did he hold that position?
Self-contained rewrite: How long did Camille Saint-Saëns hold the post of organist at the Parisian church?