Conclave, by Robert Harris (2016)

Conclave is not a typical historical novel. Although there's a historical background for the novel's fictional events, the events themselves are presented as present-day. Historical characters are also used to provide historical background, but none appear in the story's events. The setting (Vatican City in Rome) is certainly steeped in history, as are all the myriad details of the process by which the Church of Rome elects a new Pope - known as a conclave.

The novel's structure is more that of a crime/mystery novel. Like Harris' earlier An Officer and a Spy, the main protagonist is faced with a mystery (several interconnected mysteries, actually) whose successive solutions build to a dramatic climax, followed by the denouement. Agatha Christie would be proud.

The investigator is the Dean of the College of Cardinals, the Vatican official charged with running the papal election. No spoilers here, so suffice it to say that the mysteries involve the various leading papal candidates, and the writing is so skillful that it's unlikely readers will see the surprise ending coming.

The five criteria:

1. Did the novel inspire me to further historical research?

Yes. No matter how you feel about the Church, its byzantine history makes for great storytelling. More than historical events, however, Conclave made me want to visit Rome again.
Score = 4

2. Did the novel include enough history to make it an interesting historical story?

Yes. Harris provides a wealth of historical background that makes the fictional characters and conclave events seem entirely plausible.
Score = 5

3. Was the depiction of historical events accurate?

Yes. Harris was granted extensive access to the people and places inside the Vatican, which he turned into accurate detailed descriptions of papal elections past and (fictional) present.
Score = 5

4. Was the depiction of historical characters accurate?

Yes. None of them were more than background, however, so not much detail was required. Many readers will prefer this approach to the type of historical novel where the writer has to invent fictional dialog for historical characters.
Score = 4

5. Were the fictional or fictionalized plot and characters plausible?

Yes, very plausible, although becoming progressively more unlikely as the drama builds toward its climax.
Score = 5

Helenic Traders series (2002-2015), by H. N. Turteltaub

Until recently better known to me as the science fiction writer Harry Turtledove, H. N. Turteltaub (one of several pen names) is a fine historical novelist. In the four-book Hellenic Traders series, two cousins from the isle of Rhodes sail (and row) the Mediterranean in pursuit of trading profit, finding adventure and meeting many people both famous and infamous.

1. Over the Wine Dark Sea (2002). Set in the year 310 BC, cousins Menedemos (captain) and Sostratos (supercargo) embark from Rhodes with a hold full of luxury goods, including a troublesome but rare and therefore valuable peacock and several hens. Menedemos, though not a scholar, loves to quote from Homer - hence the novel's title. Menedemos is also the more amorous of the two, with a particular weakness for other men's wives.

Quieter and more introspective, Sostratos has studied in Athens at the feet of successors to Aristotle, and loves to confound his more traditional cousin with "scientific" ideas. Dialogues between the two give Turteltaub opportunities for exposition on ancient Greek philosophers and historians.

Those were perilous times for traders, with warfare between two or more of the generals (collectively known to scholars as the Diodochi) who had divided the extensive empire of the departed (323 BC) Alexander the Great. Even more dangerous for sea traders, the general disorder had allowed pirates to flourish all over the eastern Mediterranean. The traders discover that things are no better in the west, when they reach the Bay of Naples just in time to be attacked by part of a Roman flotilla on its way to raid Samnite-held Pompeii. Deciding, after a perilous escape, against proceeding farther north, the cousins head back south to go back around the horn of Italy - just in time to become embroiled in the siege of Syracuse (Sicily) by Carthage, in the Third Sicilian War.

2. The Gryphon's Skull (2002).  In the following sailing season, spring of 309 BC, the cousins set out again from Rhodes, with a new cargo of Rhodian perfume, silk from Cos, wine from Chios, and Palestinian balsam obtained from Phoenician traders. Soon added to the normal trade goods is something Sostratos finds irresistible - the fossilized skull of a horned dinosaur. Having no knowledge of either dinosaurs or fossilization, Sostratos theorizes that the skull might have belonged to the legendary Gryphon. Since no one has seen such a thing, Sostratos resolves to take the skull to Athens, to hear what the great philosophers think of it.

War, in this year between Diodochi rivals Antigonus and Ptolemy, again adds danger to the voyage, along with the ever-present pirates. Circumstances conspire to prevent the traders from reaching Athens, but the resourceful cousins still survive several scrapes and still manage to return home with a tidy profit.

3. The Sacred Land (2003). Dealings and conversations with a Phoenician trader living in Rhodes convince the cousins that their next trading voyage should head south and east to trade with the Phoenicians at their home port city of Sidon. Sostratus prepares by learning some of the Aramaic language spoken in that country. Once there, Menedemos trades in the local markets of Sidon while Sostratos mounts an overland expedition to the territory of the mysterious and insular Ioudaians (Judeans), to trade for rare and expensive balsam. The journey leads to Jerusalem and on to Engedi, an oasis at the southern end of the Dead Sea, where the best balsam is grown and processed. Adventures ensue, and readers are introduced to another corner of the ancient Greek world.

4. Owls to Athens (2015). The title is the ancient Greek equivalent of "coal to Newcastle" or "ice to Eskimos". Also, a bit of a pun - the coins minted in Athens at that time featured the image of an owl. In this fourth sailing season of the series, the cousins finally reach Athens, where Sostratos studied philosophy for a time before economics required him to return to Rhodes and take his place in the family trading business. Most of this novel takes place in Athens, where the cousins witness a sudden and nearly bloodless invasion by the forces of Antigonos, who seize the ancient city from the rival general Cassander. Once again, the cousins navigate the perilous times and return successfully to Rhodes with a cargo of silver profits.

Expecting more entries in this series, possibly culminating with the 305-304 BC siege of Rhodes. All 4s and 5s in the '5 criteria' so far.