Read this and answer the question. If the question is unanswerable, say "unanswerable".

St. Patrick's Street, the main street of the city which was remodelled in the mid-2000s, is known for the architecture of the buildings along its pedestrian-friendly route and is the main shopping thoroughfare. The reason for its curved shape is that it originally was a channel of the River Lee that was built over on arches. The General Post Office, with its limestone façade, is on Oliver Plunkett Street, on the site of the Theatre Royal which was built in 1760 and burned down in 1840. The English circus proprietor Pablo Fanque rebuilt an amphitheatre on the spot in 1850, which was subsequently transformed into a theatre and then into the present General Post Office in 1877.  The Grand Parade is a tree-lined avenue, home to offices, shops and financial institutions. The old financial centre is the South Mall, with several banks whose interior derive from the 19th century, such as the Allied Irish Bank's which was once an exchange.

Why does the General Post Office have a curved shape?
unanswerable