The obelisk in front of St. Peter's Basilica, transported from Egypt by Emperor Augustus, was re-erected in its current site in 1586 by engineer-architect Domenico Fontana. During the middle ages the gilt ball atop the needle was believed to contain the ashes of Julius Caesar - a rumour Fontana had already dispelled by examining the item himself, apparently without Quixote's knowledge.
The tomb of Emperor Hadrian was erected on the bank of the Tiber between 135 and 139 AD, housing not only his own remains but those of succeeding Roman emperors until early in the next century. The building was variously looted or repurposed over the years, and by Cervantes' time it had been converted into the fortress now known as the Castel Sant'Angelo. Connected to the Vatican City by a fortified walkway, it has provided sanctuary for numerous popes who found themselves having to suddenly vacate the premises.
The Mausoleum at Halicarnassus was constructed in the mid-fourth century BC, housing the remains of and taking its name from the classical ruler Mausolus. Built by some of the age's most esteemed sculptors and craftsmen its beauty was legendary - as Quixote notes, it was designated one of the 'Seven Wonders' of the ancient world by Greek scholar Antipater of Sidon. By the fifteenth-century the elements had taken their toll and all that remained were its foundations, which can still be seen today.