Fishbourne Roman Palace, Britain’s largest Roman villa, Lewes Castle, an 11th-century Norman fortification, and Michelham Priory, a historic house and garden near Hailsham, are at risk of permanent closure due to the coronavirus pandemic.
The Sussex Archaeological Society launched an urgent fundraising appeal on June 16 as part of its Celebrating 175 campaign.
Two weeks on, it has raised £23,145 of its £1m target, with the highest individual donation standing at £5,000.
A number of the donors’ messages referenced the Roman Palace, with some donations coming in the form of dollars, highlighting the sites’ national importance.
Roman Palace property manager, Melanie Marsh said: “We would like to thank everyone who has donated so far for their amazing generosity.
“People can support us in other ways, too. They can visit those properties that are able to reopen soon, or they can join our society as members.
“We would also welcome other fundraising ideas, such as sponsored walks or cycle rides, which would help us ensure that the society can continue to celebrate and share the heritage of Sussex, as it has done since 1846.