Just because a bell-tower, or any other building for that matter, resebles a stupa it doesn't make it related to a stupa. As you may well know, there are different styles of stupa throughout Asia, but it is their function that makes them a Buddhist building. A bell-tower has just a bell in it to warn people, no relics, no religious rites, no concept of enlightenment at all.
Saying "somewhere" and "some older books" are not references. It takes historical and archeological records to establish a theory. Does the Kalachakra tradition say anything about the Roman empire? If so, where?
You may think as you please, just don't expect me to take it seriously when it lacks proper foundation in reliable sources.
You should be able to understand that often in human history there has been a dominant culture and simultaneously there are underground cultures that manage to survive, and which also manage to transmit their teaching and their method to the next generation, and so on... This causes that their mode of existence is different than it would be as a dominant culture.
Well known example is sufism under islamic rule, and there have been many many underground spiritual cultures in Europe also. Information about them is often scanty and also quite distorted.
It also means that under such circumstances buddhism (if you can call it buddhism in such circumstances?) has been exclusively an oral teaching, and if there have been any written forms, they need oral explanation in order to be understood at all.
If it does produce the state of enlightenment it truly is buddhism. But you seem to identify "buddhism" as only a set of outer forms it has taken as a dominant culture.
If you want to see it that way there certainly are things in Kalachakra that remind one of the Roman empire, like instructions for making catapults, etc...
India is known by different names, like Bharat, Aryadesha etc... the same for Rome.
Having seen established facts disappear before one's very own eyes, I've come to hold the view that reality and history are mind made, artificial, and fabricated. Disappeared facts are replaced by new facts, they are taken to be true by the masses. Slowly what actually happened disappears completely. The masses have no chance to doubt the samaya of what is told by reliable authorities is really true. Thus with the help of this true samaya reality is created, is made, and is achieved.