> ## Documentation Index
> Fetch the complete documentation index at: https://cambridgebattlecode-mintlify-api-updates-1773706170.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# Road, Barrier & Marker
> Utility buildings — walkable paths, defensive walls, and inter-unit communication.
## Road
Walkable tiles for builder bots to move on. The cheapest building.
| Property | Value |
| --------- | ----- |
| HP | 10 |
| Base cost | 1 Ti |
| Scaling | 0.5% |
## Barrier
Cheap, takes up space, and has high HP. Useful for blocking enemy paths or protecting key buildings.
| Property | Value |
| --------- | ----- |
| HP | 30 |
| Base cost | 3 Ti |
| Scaling | 1% |
## Marker
A tile containing a single **unsigned 32-bit integer** that can be read by any allied unit. Building a marker is completely free and does **not** cost action cooldown — you may place at most one marker per round. Markers cannot be placed on wall tiles.
Any team may build over markers, destroying them.
| Property | Value |
| -------- | ----- |
| HP | 1 |
| Cost | Free |
Markers are the **only form of communication** between allied units. Global variables are not shared between `Player` instances — each unit has its own isolated Python environment.
All units (core, builder bots, and turrets) can place markers — not just builder bots.
```python theme={null}
# Write a value to a marker
if c.can_place_marker(pos):
c.place_marker(pos, 42)
# Read a marker
building_id = c.get_tile_building_id(pos)
if building_id is not None:
if c.get_entity_type(building_id) == EntityType.MARKER:
value = c.get_marker_value(building_id)
```
### Communication patterns
Since each unit's `Player` instance is isolated, markers are essential for coordination:
* **Scouting reports**: Write enemy positions to markers near your core
* **Build orders**: Use marker values as state machine flags
* **Territory claims**: Mark tiles to avoid duplicate work