In India, authorities are investigating warnings that the famed Taj Mahal monument is tilting. The 17th century monument is located in a crowded north Indian city.
Four tall minarets stand on the corners of the pearl-white marble tomb, built by Mughal Emperor Shah Jahan on the banks of the river Yamuna, in the northern city of Agra.
But the river is now reduced to a trickle, and its bed is nearly dry. Two historians are warning that the river was an integral part of the architectural design, and helped to stabilize the marble dome and minarets.
Historian Ram Nath explains that the Taj needs a full river to maintain its balance. Without that, the minarets are leaning.
"The entire Taj Mahal structure is depending on the prevalence of abundant water just below it," said Ram Nath. "If water is depleted, the building will continue to incline, or so to say, to sink into the river, because a vacuum has been created."
The state government of Uttar Pradesh has asked a seven-member team of technical experts to examine the warnings.
So far, experts are saying that the monument is structurally sound, with eight-meter thick walls and even stronger foundations. It was built over 20 years by more than 20,000 laborers, and has been called a monument "built for eternity."
But architects also say changes in the composition of the soil can hurt any structure, no matter how strong.
Pressures of modern development in the crowded city where it is located have already had an impact on the Taj Mahal.
Its marble started getting discolored due to air pollution. That prompted authorities to shut dozens of factories using coal for fuel and a search for clean energy in the city.
R.P. Perera, cultural officer at the New Delhi office of UNESCO, says Indian authorities have done a satisfactory job of preserving the monument.
"A lot of precautionary measures have been taken to prevent yellowing of the wall," said R.P. Perera. "A lot of effort also has been made to prevent pollution getting in."
Indian authorities recently observed the 350th anniversary of the Taj Mahal.
Nearly three million visitors come every year to see the Taj, drawn both by its architectural and artistic beauty, and the romantic story of an emperor who created this splendid structure for the wife he loved.