Building a tower allowed Benjamin to be better seen. The implication, however, is that he could be better heard as well. If we accept a Mesoamerican setting for the Book of Mormon, there is an interesting possible context for building this tower.
The first is that many Mesoamerican builders paid attention to acoustics. Someone speaking from one temple could be heard in the accompanying courtyard. Since the people had come with their sacrifices, it is logical that there was already some type of temple or sacrificial structure available. For some reason, however, it was not sufficient and, therefore, a tower was built.
A second interesting aspect of building this tower is that when Benjamin’s son Mosiah2 spoke to an even larger gathering, there is no mention of a tower being built. This leads to speculation that may or may not be relevant to the text.
In the location of Santa Rosa which John L. Sorenson has suggested might have been Zarahemla, a new temple was constructed about the time period when Benjamin’s speech would have been given. In that temple the underlying structural foundation had two types of rocks in the fill: one, smooth river rocks, and the second, rocks with sharp edges. The two types were clearly divided into east-west parts with no river rock mixing with the sharp stone. The whole was then plastered over and the temple built above. The non-Latter-day Saint archaeologist doing the work suggested that it symbolized two peoples joining together into one new people.
While it may be only coincidence, the idea that Benjamin build a tower on the site, where a new temple was to be built to commemorate the unification of the people of Zarahemla and the Nephites into the new people, is tempting, particularly since that is the theme of Benjamin’s speech.