I think most pepple think aliens would travel across our own galaxy, but i find that to be unlikely. Teh theory of relativity says that as the speed of light is approached mass increases, which I doubt most (known) living creatures could withstand.
I think it is more likely that we would get visitors from the Multiverse, or a "parallel galaxy" However I also think that if such travelers existed, it would be highly improbble for them to be able to return to their own galaxy, or if we discovered how to travel through the multiverse it would be highly improbably to be able to return to our own galaxy of origin, but to the infinite number of possible universes in a multiverse.
So, alien explorers may be possible, but unless they choose to spend an extended time in our universe before moving on or tryign to return, multiple visits by the same species or individuals are very unlikely.
There are reported sightings as far back as ancient times with some of our founding fathers being some to claim having sighted such occurrences. I'm an avid watcher of Ancient Aliens on the History Channel in which they provide some rather good arguments to their existence. There's a lot of past civilizations that have rather common structures, artifacts, art, and writings that are so relative to each other in a time these civilizations couldn't have possibly know each other to come so close to resemblance. When in the past what other explanation is there when people claim a flying dragon spewing out fire ascending with a leader such as China or from the books of the bible and other civilizations around the globe? With no other words to put to the technology they were witnessing. I watched a video yesterday of a navy pilot following UFO's recently. Part of documents of a program the government is claiming to have canceled. Described as tic tac shaped, then suddenly whisk off the radar screen after a period of time. There's plenty of evidence to assume we have something/one from possibly some other planet visiting our planet. If you're interested, look up Harry Reid and the UFO program.
I think it is close....take off the 'tronaut' add an 's'...and I am comfortable with a religion that believes some drunken alien ass spilled his beer which had some bacteria on it and BOOM monkeys. Done and done. Where's my tax free status.
Show me one piece of evidence of off timeline technology and don't claim the hammer coated in calcite, the brass bell found by the Creationist Institute or the Hematite grooved spheres that are not spheres and are natural mineral concretion. Show me a titanium bolt or screw from undisturbed strata an you will convert me. Otherwise I have to call bullshit.