Designed by French artist Jean-Bernard Metais, the 25-metre-tall arrow and hoop design draws on Cardiff's past and future.
Cardiff Council leader Rodney Berman said: “This sculpture will really complement the history of The Hayes on one side and the new development, including Cardiff Library, on the other.
“Alliance is an outstanding piece of public art that cannot be missed and will communicate visual images of words bilingually, which I’m sure will become an instantly recognisable landmark, and hopefully a place where people will not only congregate, but use as a place to meet and enjoy the full experience of the capital city.
“An important part of the work by the St David’s Partnership has gone towards improving and enhancing public spaces in the city centre.
Paid for by the St David’s shopping centre as part of a £1.5m public art scheme in the city centre, the sculpture’s hoop is partially submerged under the pavement and a mechanism is programmed to make it rise and fall in time with the tide.
It is also filled with a liquid that glows at night.
Cardiff is home to the Welsh government in Cardiff Bay and much of the media in Wales. Doctor Who and Torchwood along with other television series are filmed mostly within the City and County of Cardiff. It has the biggest media sector in the UK outside London, being home to several television studios and radio stations. It was a small town until the early 19th century and came to prominence as a major port for the transport of coal following the arrival of industry in the region. Cardiff was made a city in 1905, and proclaimed capital of Wales in 1955.