Ask HN: How to promote engineering culture in a company?

The company I work in has different departments like Mobile app dev, core engineering, data analysis, depts for different products and so on. There is generally a lot of cross collaboration at the management level but nothing at the engineering level. Engineering seems to work in Silos. Anyways, I felt the company should do something about it which, with blessing of the CTO, resulted in a Hackathon. The Hackathon was a great success and now the CTO wants to discuss more ways to improve collaboration among engineers.

So now, I want to ask HN, what has helped to promote engineering culture in your company? Are there other things you do except Hackathons? Also, for Hackathons, what frequency do you think is the best? Weekly? Monthly? Quarterly?