Marc Quinn's sculpture of the disabled artist Alison Lapper was displayed from September 2005 until October 2007.
Lapper, who was born with no arms and shortened legs due to a congenital disorder, posed naked for Quinn when she was eight months pregnant.
"Alison Lapper Pregnant" was replaced with a very different artwork - an architectural model of a 21-story building.
The coloured glass sculpture by German artist Thomas Schutte, "Model for a Hotel 2007" was unveiled in November 2007 and occupied the plinth until the end of May 2009.
Next came Anthony Gormley's "One and Other" - a "living monument" which involved members of the public taking to the plinth.
The space was occupied by different people - chosen by ballot - every hour, 24 hours a day, for 100 days.
From 2010 to 2012, the plinth was home to Yinka Shonibare's "Nelson's ship in a bottle" which commemorated the Battle of Trafalgar.
And currently in position is a giant bronze sculpture of a boy astride a rocking horse. It is called "Powerless Structures Fig 101".
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Weather forecasters say temperatures could reach 35C, beating the previous record of 34.6C in the scorching summer of 1976.
After years of political manoeuvring over the future expansion of Heathrow Airport, there has been an important development this lunchtime.