Time is like water—a force of nature that works gradually but with power immeasurable, a slow trickle that can, over time, carve massive caverns. The present often seems mundane, while the distant past fills up with myth, legend, and endless possibilities. Fantasy stories often build on that shifting foundation, imagining worlds based on real history.

Some writers of historical fiction use this trick as well, telling true (or mostly true) stories set in our magic-less universe, but playing with the idea that events might have seemed magical to the people involved. As these six novels prove, sometimes that dash of uncertainty over what’s real and what’s magical can elevate historical fact into near-fantastical fiction.

Hild, by Nicola Griffith

Set in the so-called “Dark Ages,” after Rome abandoned Britain but before the squabbling kingdoms and tribes were unified under one crown, Griffith’s novel tells the true story of the Christian saint Hild, who would become Saint Hilda of Whitby, patron saint of learning. In 7th century Britain, she is the 6-year old niece of King Edwin of Northumbria, and becomes his seer and mystic upon arrival at his court. The reality of otherworldly forces is taken for granted as real in this brutal, violent land, and Griffith plays with the concept expertly as Hild becomes increasingly masterful at sniffing out plots and advising her uncle in ways that often seem magical. Anyone who has been awed by a brilliant mind’s ability to perceive what most cannot will witness that superpower at work in Hild, one of the most complex and deeply-drawn characters to ever appear in a novel—historical, fantasy, or otherwise.

The Risen, by David Anthony Durham

Few authors embody the relationship between historical fiction and fantasy better than Durham, whose work moves effortlessly between the genres. In The Risen, Durham skates as close to fantasy as possible without crossing the line, infusing the story of Spartacus’ slave rebellion with mystical priestesses who seem able to predict future events and a real sense from the various point-of-view characters that the gods they worship are very real, and actually do communicate with them, doling out assistance—or punishment. The strong characterizations make it easy to see how, in a world without formal education and not so separated from the more primitive and less civilized age that came before, a myriad of coincidental could easily be seen as evidence of a magical world existing just under the surface.

The Cousins War series, by Philippa Gregory

Gregory has become something of a master of plausible deniability when it comes to incorporating magic into an otherwise straight-up historical fiction. Set during the Wars of the Roses and focused on three women who plot, manipulate, and scheme for power, The Cousins War is packed with people who claim magical powers or invoke supernatural forces to further their schemes—forces that seem to work often enough to edge right up to the line separating fantasy from history. The great trick here is that Gregory is often simply depicting magic before a documented historical event, similar to the way sports fans will put on their rally caps and then claim to have influenced the results of the game. You can choose to believe or not; either way, it adds a nice layer of spice to an well-crafted story.

The Soldier series, by Gene Wolfe

Latro is a Roman legionary who awakes with no memory, but is plagued by visions. While most of the people he meets in his ensuing adventures are happy to assume he’s been cursed by gods and is being tortured (or empowered) by evil spirits, it’s also easy to see another explanation: a simple brain injury. Wolfe plays with this shifting perspective like the master he is, offering a story based on historical fact that you can view as realistic or magical simply by shifting your perspective, ultimately leading you to wonder how many of the myths and legends of the past can be ascribed to mental illness or physical injury.

The Warlord series, by Bernard Cornwell

Cornwell is one of the masters of the historical novel; his stories are as exciting and surprising as any fantasy, without sacrificing verisimilitude. In his celebrated retelling of the Arthurian legend, Cornwell toes the line between history and magic not only with the reader, but with his own characters, who are often uncertain whether the “magic” used by Merlin and Nimue is a supernatural force, or a collection of coincidences—while allowing for the third possibility, that it’s a collection of coincidences caused by a supernatural force. This complexity is emblematic of the series as a whole. It will give you a new appreciation for the legends of King Arthur and the brutal world that gave rise to them.

I, Claudius, by Robert Graves

The Romans were a superstitious lot, convinced that the gods influenced every moment of their lives and could be manipulated through offerings, sacrifices, and prayers. They often believed in magic and saw it everywhere, and even Rome’s masters weren’t immune to its influence. In telling the story of Claudius, proclaimed Emperor after his nephew Caligula was murdered, Graves offers us a perceptive, intelligent man who sincerely tries to be a good emperor—but who also sees prophecy, magic, and a hidden world of spirits everywhere he looks. Graves’ peerless writing makes the often dull business of ruling an empire seem fascinating, and the hero’s tragic life will make you feel pity for an emperor for perhaps the only time in your life, even as it transforms ancient Rome into a doomed fantasy kingdom.