There Was Time

In Poul Anderson's There Will Be Time (New York, 1973), time traveling mutants are born in different historical periods. The Eyrie, a time traveler organization based in North America in the late twenty first century after the War of Judgment, wants to expand and recruit in the Middle Ages.

It is cumbersome to carry goods through time so the Eyrie plans to hijack loot that the Fourth Crusaders would otherwise plunder from Constantinople in 1204. New recruit Jack Havig had visited Constantinople in 1050 and is fluent in the Greek koine so his first mission for the Eyrie is to scout for the hijack.

An airplane takes Havig from North America to the radioactive ruins of Istanbul from where he travels to 1195 by counting sun-traverses, estimating days missed, then "...zeroing in by trial and error." (p. 93) He carries forged documents and gold to exchange for nomismae (coins).

Visiting the house and shop of Doukas Manasses, goldsmith, to learn what wealth it contains, he is invited to stay for dinner and becomes a family friend, revisiting each year as Doukas' daughter, Xenia, grows from five to thirteen, but cannot persuade Doukas to leave the city.

In order to scout the sack, Havig:

time travels to a safe date;
walks to the site of one of the buildings that he knows will contain wealth;
flickers in and out of time throughout the sack;
thus, learns what happens at each site;
if he sees Crusaders enter a building, then leave with loot, writes off that site;
if he sees a building overlooked, records the site;
if, as at the Manasses', he sees approaching Crusaders cut down by machine gun fire, records the site;
thus, is able to inform the Eyrie not of buildings that they can ransack but of buildings that they did ransack;
travels back downtime, takes ship to Crete, finds a specified location, then returns uptime;
realizes that it would have been simpler to base himself in a twentieth century Istanbul hotel.

The return via Crete is because it is not safe to cast about for an agreed-on rendezvous time in radioactive Istanbul. The Eyrie agents, dressed as Crusaders, have arranged for a ship to transport their plunder. This is how such an operation is conducted by time travelers who, by will power alone, move through time though not through space and who do not have temporal vehicles to transport goods.

We last see Time Patrol agents on a similar mission but they do have a large space-time vehicle so their task is considerably easier.