An allohistorical lure was a method of manipulating history, generally for rescue. The idea was that a time traveller would send an object back in time, which would change the history of another civilisation. The civilisation would then be drawn to the time traveller, allowing the time traveller to escape in what would appear to be no time at all.
The Arkive tried to send an allohistorical lure to the Silurians to save itself. It was a rectangular stone that glowed every third of a Saturnian year. The Arkive missed and sent the lure back 50 million years too early. Instead, the lure was found by humans in 1890. The lure was passed on through the generations, causing humans to choose Mnemosyne to colonise. (PROSE: The Wheel of Ice)